This 1990 GMC Sierra 3500 isn’t all it appears to be…and this special truck is for sale!
You know the adage about old trucks, and GMC certainly doesn’t build trucks like this crew cab, long bed GMC Sierra Square-body anymore. This truck has actually been one of the most popular trucks we feature every once in awhile on TFLtruck and belongs to our friend and occasional presenter David Morrow (check out his channel here).
Not only is the truck a rare sight in itself these days, but this truck houses a competely different powertrain than the big block 454 gas V8 and 4-speed manual that it originally came with. In fact, it has a 5.9-liter Cummins 12-valve turbodiesel from a 1994 Dodge Ram — the very same engine as TFLtruck’s own Kase Van Rees has in his Ram 2500 truck. It pairs up to a NV4500 5-speed manual transmission, making this truck pretty damn awesome for those who are in to good-old rigs without all the complicated technology of today’s heavy-duty offerings. Plus, as a firm advocate for the #savethemanuals crowd, that manual provides a driving experience you quite literally can’t get anymore in 1-ton trucks.
Even better, you can actually buy this truck on our TFLbids auction site! It’s up right now (March 16, 2023), with the auction running until next Wednesday, March 22.
Here is everything you want to know about the truck from the man himself:
In posting the truck to TFLbids, David wrote up an expansive description covering everything you probably want to know about the truck. Here’s everything he included about the Sierra:
“Truck originally came from the factory with a big block 454 Throttle body EFI Engine and a SM465 4-speed manual transmission. I bought the truck in 2014 from a local individual who lived in northern Colorado and used the truck mainly to go camping with a slide-in camper and to pull a boat.
I used the truck with its factory engine until 2016 when I started the engine swap. It took 2 years to complete the engine swap. The Cummins engine came from a 1994 Dodge single cab with a manual transmission. The block was disassembled and sent to the machine shop and the head was magnafluxed. We reassembled the block to factory specs and used ARP head studs, so it is set up for big power if wanted. The P7100 injection pump was sent to Industrial Injection for a complete rebuild and upgrade. The pump now has a new larger cam with 191 delivery valves.
The AFC housing has been modified with parts from Power Driven Diesel with AFC live and a max travel kit and has 3000 rpm governor springs. The current turbo charger is a Borg Warner K27 which is a very good match for the power and fuel setup. The timing is set a little greater than stock. I believe we set it at 20 degrees. I just installed new 5 x11 injectors from PDD about a month ago. They are only slightly bigger than stock.
The GM engine cross member was removed and replaced with a new cross member made by Screamin Seaman. It utilizes motor mounts from a third gen Cummins truck and made the installation of the 12 valve Cummins very easy. I’ve been very happy with the look and quality of the whole engine mount assembly. It looks very professional. The transmission mount is the original GM crossmember that the truck came with and the NV4500 bolts right up to the original rubber mount and looks very factory. All of this made the driveline angle just perfect and I have never had any driveline vibration ever.
With the installation of an NV4500, the shifter location was moved back towards the seat by 6 inches. I had to cut a new hole in the tunnel and patch the old hole. The new shifter location is actually very comfortable and is better than the original location. I used the Dodge shifter boot and just flipped it around and put some sound foam inside. It works great. Sound deadening material was used throughout the cab, as well as under the hood.
The stock water pump and power steering pump were used, but the a/c, alternator and brackets are not stock. Because of the narrow frame of the K30 GMC, the A/C had to be relocated higher in the engine bay. I don’t remember the manufacturer of the a/c and alternator, but both are high quality units that have worked great. The only issue I have had with all of the belt assembly is alignment. The alternator is just a hair out of alignment, which created a squeal until one of the ribs on the belt wore off. Now it has no squeal and has been squeal-free for 40,000 miles.
The lift pump and heater were removed from the block and replaced with a FASS Fuel system that has a straw pick up tube in the driver side fuel tank. New supply and return lines are clamped to the inside of the frame rail and is protected from wear at key spots. FASS is a very good fuel delivery system; however, in very cold weather the water separator filter will freeze and block fuel delivery. Because of this issue, I rarely use the truck when temp is below 20 degrees.
FASS does sell an electric heating element to fix this problem, but I have not spent the money to remedy the problem. I drive my gas truck in the cold, snowy weather.
It was important to me to retain the core support and grill, as well as the radiator and a/c components. To retain the big block radiator, I had to install a larger inlet and outlet on the radiator, so I had a radiator shop clean and refurbish the big stock radiator at that time. When installing the block, I was able to massage the firewall back far enough to allow the stock Dodge fan with clutch to fit, and still have enough room to spin the fan off, if needed. I was able to cut and fit the GM fan shroud to fit and this has made cooling very efficient. It has never had a problem with cooling, even when pulling my camper.
By keeping the stock core support up front, it did make it difficult to fit an intercooler. However, I managed to find an after market intercooler with a 3-inch inlet and outlet to fit. This is not the most ideal size for the Cummins, but it does work and allows the truck to maintain the stock grill, lights and blinkers, which was a big deal for me.
The transmission is also from the ’94 Dodge donor truck. It is a NV4500 manual with overdrive. It was completely rebuilt with new syncros and bearings and mated to the GM NP205 transfer case using an Advanced Adapter plate. This necessitated lengthening the front drive shaft by 4 inches and shortening the rear drive shaft by 4 inches. They were cut and balanced by a professional shop and new U joints were installed.
The axles were left unchanged with new gear oil and service. However it has a brand new Red Head steering box and a dropped pitman arm. The steering stabilizer is fairly new and the truck drives very straight with only slight wandering, consistent with most GM solid axles. I also replaced the lock outs with new Warn lock outs.
The suspension is where I spent some money. I purchased new custom springs with greaseable shackles from Off Road Designs. This change in suspension improved the ride dramatically. It was well worth the money for new leaf springs on all four corners with new U bolts and shackles. At that time, I put new Bilstein shocks on all four corners, however, the front shocks take quite a beating with the heavy Cummins up front, so I think the new owner would do well to install some bigger shocks up front. The truck does have air bags on the rear when you are carrying a heavy load. They can be filled individually with 2 Schrader valves.
The exhaust system is all 4 inch pipe front to back that I built and welded myself. It’s decent looking, but wont make it into any how to video. There may be some baling wire in strategic places.
The gauges in the dash are all original and I was able to mate them to the Cummins with no problems. The fuel gauge is a little strange, but it is pretty reliable when it registers empty. I installed a tach on the steering column that is gauged off of a magnet on the harmonic balancer and works just fine. EGT and boost gauge on the dash are pretty cheap, but they always work. I cleaned up a lot of the wiring that was no longer needed (12 valve Cummins’ are so simple) and it makes the engine bay look very clean. While I was under the dash I replaced the heater core, which is prone to failure. The radio is original to the truck and works just fine. I did replace the rear speakers with some slightly better ones.
Fuel tanks are in great shape and both work fine; however, I did make a big change that has worked great for me, though a little unorthodox. I disabled the switch on the dash, which is prone to failure, and connected the tanks together using a 2-inch hose with a ball valve between the tanks and built a steel crossmember to protect the hose which allows me to have 40 gallons of diesel on board. I am able to fill both tanks from either side by simply opening the valve between them. The only downside to this setup is if both tanks are full and the ball valve is open, if you are parked on an angle the fuel will overfill one side or the other and leak out of the cap.
Two batteries was a must! So I found a stock battery tray for the driver’s side and ran large cables to connect the two. I also made sure to install as many ground wires as I could, and installed a new fuel shut off with connectors. I did delete the grid heater but did install a block heater. Since I don’t drive the truck in the winter very often, it is not an issue. This truck always starts.
This truck does have a fairly new trailer brake controller that works great. The brakes were redone when I built the Cummins, however, that was 45,000 miles ago so the front brakes may need some attention in the near future.
The tires are top-of-the-line Michelin Defenders with about 40,000 miles on them. I suspect they still have another 30-40k left on them. Truck drives fairly straight and front end is in good alignment. Have never had a problem with tire wear.
As you can see in the video, the interior is in fairly decent shape for a 33 yr. old truck. The dash is very cracked but looks good with the blue cover on it. The windshield has a couple of cracks and could use a replacement. The front seat has significant wear and tearing. I was going to install bucket seats at some point, but never got to it.
Bench seats are nice so you can have your girl slide over next to you. The glove box opens just fine, but when you close it you have to turn the latch to get it to lock. My custom headliner is still pretty cool, but is starting to sag in places. All the trim that holds the headliner in place is all there, but a few of the plastic pieces have broken. The gauge cluster plastic has a couple of cracks where it mounts to the dash.
The exterior is almost rust free with just a few small surface rust spots. The front inner fenders both have a rusted through spot on both sides. Though barely noticeable, I did cover the two spots with aluminum plating. The tailgate is in rough shape. It is dented on the top and has a slight bow, but it still works as it should. The bed is in decent shape, but has large areas where the paint has been rubbed off. The front of the bed is bent in towards the cab, which has made a gap where you can see the ground below.
All the doors shut and latch very well. However, the drivers door has a slight sag, which makes the body lines just a bit off. The windows all operate as they should, though the driver and passenger side front windows are both difficult to roll up and down due to the worn and sun- baked trim and rubber seals. Replacing the rubber on all the doors would remedy this problem.
This truck is a real gem of a truck! Even with its cosmetic defects, it is still a head turner! I have spent my dollars on the drive train to make this a very capable beast. It could use some love on the interior and exterior to be a real beaut! But it will take you where you want to go. I have spent countless hours putting this engine and drivetrain together to be worry-free, however, I make no warrantees or guarantees on drivetrain or chassis.
It is important for you to know that this truck has never had to go through an emissions test or a safety inspection. I registered it as a farm truck here in Colorado and neither are required for a farm truck, If you are going to register it where it may need these inspections, please note that I make no warrantees for this. It is your sole responsibility to make any corrections to the truck to bring it up to your states requirements.”