So i got a 04 chevy 2500 with mbrp exhaust and everything else stock and my trans was not shifting right and wont go into gear and i was retarded and didn't wright down to code but when i erase them the problem went away any suggestions what it could be?

does it wait a while and then shift into gear...is it real jerky and bad going into 5th?????had a similair problem to it to local dealer they told me that it was a wireing harness going into the injector modual...wire had started to eroad out....they fused it together and havent had a prol since....but i had no problems when my light wasnt on but when it was the tranny was a bear