Hi! I have a 97 f150, with 240,000 miles...I recently had a lot of front end work done - upper and lower ball joints, stabilizer links replaced, idler arm, had an alignment done, after they put the steering wheel back on straight (after having gear box replaced, it wasn't on straight)....recently, I pulled in my driveway, put truck in park, and it started rolling backwards! It doesn't do this going forwards, just backwards if I'm on any kind of incline...any assistance would be greatly appreciated!!

 

Sounds like your park mechanism or linkage in the transmission is in need of repair, replacement or adjustment.