Have a modded LT1 Caprice with hot Cam, 2400 stall torque converter and 3.73 gears.
I don't like 3.73 gears for all-around driving and am trying to swap them for a highway gear, either 3.08 or 3.23. They don't feel right on the highway, too high RPMs for my taste and MPG is horrible, I got less than 18MPG. I know the B-body can do much better than that.
3.73 work OK up to about 50MPH, mixed city driving but get the engine noisy on the highway. Go 70-80 and the RPMs will be around 2400-2700.I had another B-body with LT1/2.93 and thought that it was a bit too low (numerically). But it did get 23MPG on the highway. Stock LT1 Impala SS came with 3.08 gears or 3.23 if it has the L99 engine.
I had an L05 Caprice with 3.23 and thought that was OK, a good compromise gear for all situations. Now of course L05 was only rated for 180HP versus 260HP of LT1 so I wonder if I can get away with 3.08 now. I plan to run 245/50/17 tires on stock SS wheels.