GMC used a 324 Olds V8 in 55 and 56 and a 371 Olds in their 57 to 59 trucks. It was limited to the 550 and 650 series trucks. Chevrolet used a 322 Buick engine briefly. Actually Chevrolet came out with the first true General Motors truck engineered V8 with the 348 in 1958. My theory is that GMC was already toying around with their V6 and that is why they they didn't really develop a V8. They did come out with a 637 V8 in the early 70's, but it was already a Diesel world by then. Chevrolet dominated the gasoline powered truck market with the 348 and 409 in the 60's. GMC lost a lot of market share in the 60's because of their V6 and not offering anything but a Detroit in their larger trucks. By the time they offered a Cummins in the mid 70's, their market share was lost forever.
