I have 3.73s in a daily driver and love them,but traction is an issue. Just get a good set of tires and throw them in. If you do a lot of highway driving go with 3.55s.
I have 3:73's love them. Came with the car so I didnt get to feel the difference between stock and aftermarket. I say go with 3:73's they work good with a stock car mine was when I got it.
I daily drive on 4.56's. I love it. She really winds up on the freeway. It doesnt feel all boggy like overdrive usually does, it actually rides in the powerband. I havent measured the milage but its quite good amazingly. Shooting from the hip, I'd say like 20 mpg highway with a carb, 4.56's and an automatic it's not bad.
See, gears HELP your milage since they make it easier for the car to push itself around. You start to lose milage only when you run out of gear near the top and are rolling around at a higher rpm. Even then, the highway cruising at 2700 or so doesnt seem to slurp the gas by much.