[grfnkl]

Well your on the right track by having it checked for codes. When's the last time you had a trans fluid changed? There may be some dirt build up causing some problems. It also could very well be one of the vacuum lines or connection that's causing this and there is always a possibility that's it's not even tranny related, such as a bad computer, clogged catalytic converter, and so on... let us know if there any other symptoms that could help diagnos this better.