What automatic transmission? How are you planning on using the truck? If no load hauling or trailer pulling then a Turbo 350 or 400 transmission coupled to a 3.08 rear end should be fine. If your going to use it as a truck then a rear end with 3.73 or 4.11 and an overdrive transmission will be a much better combination. Even with the load pulling 4.11 gears the final drive will be 2.75 in overdrive so it's sips less fuel than the 3.08 behind a non-overdrive trans, the best of both worlds.
