3.73 Gears?

I called one place and they wanted $425 to instal my 4.10's and they wouldnt warranty 'em cuz I didnt buy the gears through them. crapola

But if you have a decent tire in back and "learn" how to drive with the extra gear you'll be good.
 
How much do 3.73's change your RPM's. I normally just drive around town and stuff, but I go back and forth to school quite a bit on the beltway so I'm cruzin at like 75-80 for a half hour or so. I have a decently loud exhaust, so if I'm going like 60 or 80 with 3.73's, what RPMs am I gonna be at? Also, will a ford dealer let you keep your warranty if you get the FRPP gears and have them install em?