I am new to the 350z arena and am about to buy my first 04' 350z and first 6 cylinder, I own a mustang 5.0.

one of the best mods for stangs are the rear gear change to a lower gear
does this mod also help the Z accelerate more quickly like other cars,. the problem Im seeing is that the car is an auto and everywhere ive read they say that the gears are for manual trans only. can the swap be done to an auto and what would still be ok at traveling at 70mph on the highway? ive seen 3.9 and 3.7 gears that may be a good option

let me know what your opinions are

I plan on adding u/d pulleys , intake and exhaust changes too

thx in advance - steve