a little off topic, but I loved the royal purple I had in my car for 2500 miles. Everything was great, and I've tried alot of different synthetics. I'm well on my way to becomming a conossieur in such matters.
In terms of gears, one of the best arguments I read when I first joined the forum was that with the higher gears, you car has an easier time accelerating, and will therefore use less fuel. Your ECU will run a little leaner under NORMAL driving conditions since it requires less effort to accelerate. I can't state the argument as well as whoever I heard it from, but I'm sure he will voice up soon. good luck, and go with the 3.73's. I seriously doubt you will regret it.
2000 automatic gt-
borla cat-back, bassani x-pipe w/ cats, steeda MIL's, k&n fipkit, cobra calipers up front, wolf springs, KYB adjustable shocks, C&L intake plenum, MAC 70mm throttlebody, kenny brown subframes w/ cross brace, plasma booster, SLP 180 degree thermo, frpp 3.73's, superchip custom tune
new #'s - 241 rwhp, 290 rwtq