First you need to do 3 things;
1) Find which trans you have, is it all aluminum (2sp) or iron front case/alum tailhousing?(3sp)
2) Find the axle ratio, it may still have the ratio tag on a centersection bolt or jack up one side and count the rotations. (it's probably a 3.56)
3) Find rear tire size, measure the diameter or curcumference. (you can get a 10% overdrive by putting 3" taller tires on rear to equal a 3.20)
I'd borrow some tall tires first to see if you are happy w/the change in rpm's.
Changing the trans to anything non stock is the most expensive and LEAST desirable way to fix this problem! (unless your switching the aluminum 2sp for the iron 3sp. Thats just a bolt-in.)
Let us know what you find out.
p/s fixing the exhaust may make it feel like less rpm's also.......
Regards,
Ron.