Will I regret change to 3.55s from 2.76s

Putting 3:55 gears I. Where you had 2:76 will make it feel like a new car, but crazing at over 70 mph would be marginal deal. As far as gas mileage, I have a 340 six pac with 3:55 gears, it will supposedly get close to 20 mpg if I keep my foot out of the throttle, i have never been able to actually find out, lol!