If you change gearing, most people recommend at least two levels, so 3.73 -> 4.56. I agree the 6-spd helps tremendously for accelerating. It does nothing for highway cruising when the torque converter unlocks or the trans drops a gear for overpasses. Get the tires first, and evaluate the performance before deciding.

4.56 in 6th gear and 35" tire will turn about 2425rpm @ 80mph. You don't want to go much faster with a lift and 35" tires, but 100mph is about 3000rpm.