Alright so for about a month now my OD light keeps flashing on/off when i start to go up a hill it shifts into over drive and then back out again. Also sometimes when the truck shifts it will shift into over dirve then into the next gear????? have no clue wear to start?

 

The best thing to do is take it to a transmission shop or the dealer and get the code read. The flashing O\D light is sort of like a check engine light. It will be much easier to diagnose\repair the issue if you get the code read.