I had the same problem after my 96 was hit in the front left corner, after i got the truck back from the dealer the light came back within 4 days, took it back and said it was my gas cap, not believing it i replaced it and the code came back, I did some searching and found my fuel vapor management valve was cracked around the clips, it is kinda a pain to get to, it is under your batery, remove your battery and tray then you will see it, it has two or three vacuum lines to it and to bolts securing it, 5/16 i believe, remove it and inspect it, it could have also poped open all it is , is a little diaphragm with a spring and an o ring, if it is bad it will cost you around 60 bucks. hope this helps, also check all you lines from the gas tank up the drivers side frame rail to the inder hood compartment.