as mentioned, first thing to do is check the transmission fluid. check it warm and running in park, if possible or unless the instructions suggest another method. NEVER over-fill it. you're better off a little low than a little high on the fluid level.
if that doesn't do it, have the kick-down cable (if equipped) checked / adjusted. next thing to have checked up on is the 'band adjustment', not something that can be done without some effort. best to take it to someone that specializes in transmissions.
it could also be caused by a clogged filter or worn seals on the governor.
many late model transmissions use a control unit, this can be scanned for error codes.
EDIT-
by the way, there are many Haynes books 'about' cars.
http://tinyurl.com/5gobn