You gotta check this out! This is a rare 1990 GMC 3500 one-ton crew cab 4×4 “square body” truck that is in pretty good shape. This truck is more special because it is a Cummins 12V 5.9-liter I6 diesel engine swap. The engine, transmission, and the suspension are fully rebuilt. It also has a customized bed with a custom bed-step in the back.
Cummins 12-Valve Swap
This is a 1990 GMC 3500-series crew cab truck with an 8-foot bed. David (the owner of this truck) purchased it several years ago for about $4,500. It had a 454 cu-in gas V8 and a 4-speed manual transmission. It was a working truck, but it go about 10 MPG and lacked power in the mountains.
Some may call it a “Gummins”…
The 12-valve 5.9-liter Cummins I-6 turbo-diesel engine is the solution for this truck to get more power and more efficiency for big and heavy work truck. David bought a beater 1994 Dodge Ram truck as the engine/transmission donor. Next, the engine and the 5-speed manual got a rebuild with upgraded parts for more power and durability.
Here is a partial upgrade list:
- Arp head studs
- 3rd-gen Cummins motor mounts
- Freightliner Cummins bracket for a/c and gm compatible alternator
- Dual batteries
- Fass fuel pump with filters
- New intake and intercooler
- New BorgWarner s300 turbo
- Big AFE air filter
- Performance built P7100 fuel pump with 3000 rpm gov springs
- New 4” exhaust with 2 pass through mufflers
- Bigger injectors
- Power driven diesel AFC live fuel management
- Upgraded a/c compressor
- Gauges for tach, EGT, & boost
- New progressive leaf springs on all four corners with greasable heavy duty shackles from Off Road Design
- Bilstien shocks
The original 12V Cummins 5.9-liter from 1994 had a rating of 175 hp and 420 lb-ft of torque when paired to a manual transmission. This updated, rebuilt, and modified engine is making closer to 300 horsepower and unknown amount of torque.
David says this 8,000 lbs truck now gets about 21 MPG on the highway at about 65 MPH. That’s about double the efficiency of the original gas V8.
David says: “I’ve put about 10,000 miles on it and worked it hard. Pulled my bobcat up in the mountain a few times. It pulls as fast as I want to go and stays very cool on temperatures.”
This truck also has a custom tail-gate step. It’s a not a Multi-pro tail-gate as on the 2020 GMC HD, but it does the job in much the same way.
We all want a big, comfortable, and capable truck, but new heavy duty diesel trucks range between $60,000 – $90,000. David, says the truck, the swap, and all the modifications total about $24,000.
In the end, this is a diesel heavy hauler that will be working for years to come at a fraction of the cost of an all-new truck.
