Weird Shifting

I JUST PURCHASED A 94 351 XLT, with high mileage. when i test drove it, it shifted great. but now every so often it will rev higher then normal and shift hard. i told the guy i bought it from and he thought it was a valve hung up. he had it flushed and new fluid put in, but it still does it, can some1 help??

Depending upon the transmission in the truck (some are electronic), your throttle valve cable may be binding. Check to see if there is a cable running from the throttle lever to the trans. If so, make sure it pulls out smoothly and returns by itself.