personally i think 4.10's may be a bit much for an auto. unless your gunna be building a drag car. yes you should get it tuned for the gears, unless you want it to shift like a 125cc dirtbike (idk some people like that). 3.73s would be a good bet especially if you plan on doing anything big like a blower. dont waste your money on a "shift kit", you can do the same thing through a tune. and yes it does increase rpm at any given mph, thats how changing to a lower gear works. it makes a huge difference. best mod for the money imo. oh and dont worry about leaving it stock. only 141 of my roush were built and its #9 and i've done quite a bit. exhaust, intake, pulley, guages, interior parts, hood, tinted lights, wheels im sure i forgot sime stuff. but you wont enjoy it and have fun with it when its stock.