I just bought a 73 LT Z28. The last owner did the restoration and overall its a nice car. one thing he did was replace the 3.73's with 3.42 gears to make it cruise better on the highway. Took the car out tonight and it goes but I can see that the bottom end could be improved. I live about 30 minutes out of town so the taller gears is a bonus running country highways pretty much everywhere I go. How much of a difference in bottom end performance would I see going back to the original gears (came with the car)? How much higher rpm am i going to see cruising on the highway? Engine is supposed to be around 350hp and has an M21 4 speed.