I would try to stay away from the 6.2/6.5 engines. Everyone that i know that has ever had one hated them. Tons of problems with them. The new Duramax would proably be awesome, but it would be pretty hard to find one. I have drove a 2001 Dodge ram with a 5.9/automaic, and i loved it. The truck would haul a$$. If you did the Cummins, the motor mounts would proably have to be fabricated, and you might get stuck using a Dodge tranny.
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Lucas
"Another proud owner of one of the coolest trucks ever built"
drop_shift@hotmail.com
My Daily-Driver: '72 Chevy LWB Custom/10. Rebuilt 350, 300 HP thanks to a few go-fast goodies. Ochre with a white top. Future plans include a frame off restoration, and maybe a blown 383.