We heard it before we saw it—the unmistakable rumble of a 12-valve Cummins turbodiesel. But it wasn’t coming from a Dodge. When we turned, there it was—Forrest Roth’s massive 1979 Chevy K10 4×4. The Cummins grabbed our attention, but that was just the start. Underneath, a custom chassis with a triangulated four-link suspension, coilovers, and beefy Rockwell 2.5-ton axles tied the build together.

Heavily Modified Cummins, Beefed 47RE Transmission

Forrest obtained the engine from a 1996 Dodge 3500, which he purchased specifically as a donor vehicle for the Chevy’s build. The Cummins is completely rebuilt and modified to make big power. Some of its features include marine-application pistons, an upgraded camshaft, and larger injectors. Additionally, it has a 63/67mm turbocharger, modified P-pump, AirDog lift pump, and ARP bolts and head studs. But that’s not all—it also has Hamilton Cams tappets (and an Industrial Injection tappet cover), 4,000-rpm governor springs, and 60-pound valve springs. A pair of Optima YellowTop batteries are mounted under the cab between the framerails, and a five-inch-diameter exhaust carries away spent gases.

To ensure the 47RE four-speed automatic transmission would hold up to the Cummins power, it was rebuilt by Firepunk Diesel to handle 1,000-plus horsepower. Firepunk’s Anteater STC replaces the factory PCM and provides control over transmission shift patterns. Power is split to the axles via an SCS Gearbox 12-inch-drop 1:1-ratio gearbox.

2.5-Ton Rockwells With Disc Brakes, 4.90:1 Gears, And More

The 2.5-ton Rockwell axles were sourced from C&C Equipment in Nashville, Indiana. Forrest fitted each axle with disc brakes fed by a hydroboost system, a pinion brake for emergency braking, and Ouverson Engineering 4.90:1 differential gears. He narrowed the front axle by 7.5 inches and added manual lockout hubs sourced from Boyce Equipment. The front wheels are pointed via a custom hydraulic crossover steering system with RedHead steering gears. Out back, he flipped the hubs in to narrow the axle.

Remote-Reservoir Coilovers, Triangulated Four-Link, 44s

The custom triangulated four-link suspension has link bars made from 0.250-inch-wall DOM tubing. Each Big Shocks remote-reservoir coilover delivers 16 inches of travel and features an adjustable top mount for fine-tuning. The suspension creates plenty of room for the massive 19.5/44-20LT Interco Super Swamper TSL Bogger tires mounted on 14-inch-wide aluminum wheels custom-made by Real Racing Wheels.

1979 Chevy K10: Custom Chassis

The truck’s backbone is a custom-built frame. Forrest started with Chevy longbed framerails, shortened them, fully boxed the frame, and added 2.5 inches of height to ditch the need for a body lift. The custom chassis packs crossmembers made from 2×4- and 2×6-inch steel for ample strength. Down low, a hand-built drop subframe cradles the SCS gearbox and doubles as the central mounting point for the suspension link bars.

Interior And Exterior Bits

Forrest upgraded the interior with a Squarebody Syndicate steering column and gauges, Corbeau seats, and a console from a 2016 Chevy truck, among other things. On the outside, modifications include a Warn Enforcer front bumper and custom “Silverado Cummins 65” aluminum emblems on the front fenders.

In The Family Since 1979

Fun fact: Forrest’s truck has been in his family since day one. His grandfather bought it new and promptly put it to work plowing snow. Later, it passed to Forrest’s dad, who drove it for a while before gifting it to Forrest when he turned 16 in 1998. It was his daily driver through high school and has stuck with him ever since. Over the years, Forrest has rebuilt the truck several times—the latest overhaul came in 2021 and resulted in the build you see here.