No Reverse - 2002 F-150 Supercrew

My 2002 F150 Supercrew V8 w/auto transmission and 97000 miles will not go into reverse. The problem started when the overdrive light on the shifter started flashing. The next day I go to back the truck out of the driveway, when I put it into reverse it wouldn't move so I depressed the gas a little. The truck then jerked into reverse really hard. I put the truck back into park and turned it off because it scared me a little. Ever since then it won't go into reverse at all. I checked the tranny fluid after warming the engine up and the levels are fine, the fluid looks good and doesn't smell burnt. What is the problem? Any help will be appreciated. Thanks :D