Likely an issue with the TPS sensor on the bottom of the throttle body. Could be a few other things, which you might try first - I would try cleaning the throttle body with throttle body cleaner, and what's the idle rpm? A previous owner could have adjusted the throttle stop and gotten things screwed up.
i know your trucks a 95 but this is the how to on checking the tps voltage.
for a newer model. this might help you tho.
i'm pretty sure you just disconnect the wires and undo the 2 screws and put the new one in place. then follow the instructions for adjusting the new tps http://www.f150online.com/forums/lig...ttle-body.html