H
Both car are the same, 8cylinder is stronger than a 6 one.

LJ
i'm not a chevy guy but i would take the gmc no matter what. they're the same trucks basically but anything with a v8 is good.

Jeff S
Sierra with the V8 is better because it uses the Chevrolet Small Block engine. No one makes better V8 engines that GM. The V6 is pretty good (definitely better on gas) but it's nowhere near as robust as the Chevrolet Small Block, the reliability of these engines is legendary. I was able to drive an older generation Chevy V8 from Illinois to California with 2 dead cyinders and I had no problem.