Due to the very low rear end gear ratio in your truck and the slip of the torque converter of an automatic I would use an overdrive transmission if I were you. Your best bet would be a 4L-80 they are much like a turbo 400 but with a 4th gear overdrive. They can be found in mid 90s to present Chevy and GMC ¾ to 1tons and there are even stand alone computers for the electronic models. In my opinion you would be disappointed in the performance of your truck with t turbo 350 pushing though them low gears.
