how many rpm's will i drop going from 3.91 to 3.55????????????????

it really depends what you want to do with the car, for long road trips 2.73--2.94's are best, saves on fuel and wear and tear on the engine. But driving around town you will miss the 3.91's.

I'm keeping the 3.91's cause traffic here goes 35--40 mph on most secondary roads. At those speeds the 3.91's feel just right in 3rd gear and 2nd gear comes on strong for passing.

I did find a different rear end with "normal" gears at my local scarp yard but now that fuel prices are not going to $5 a gallon this year don't think I be getting it.