Tranny need to have the codes read most likely it slipping
scan the TCM for codes
March, 5, 2008 AT 8:49 PM
Check the speed sensor. It is either located on the tailshaft of the trans or on top of the rear differential housing. If the computer can't sense speed, it won't feed info to the speedo/odometer and it also won't know when to shift. O/D light will probably flash a P0500 code, but check to be sure.