4L80E No overdrive...sometimes

[oltronj]

I have a 91 Crew Cab single wheel 1 ton with a tbi 454 and a 4l80E transmission with a 205 transfer case. The issue I am having is that sometimes it will either slip out of overdrive and wont go back in or wont go into overdrive at all. When it wont go into overdrive it will not lock the converter either. It shifts 1-3rd just fine all the time and does not seem to be slipping ever. I have read that the pass through electrical connector can sometimes be cause for issues and will check that first. Just wondering if anyone else has had these issues and what was done to correct them, or if there are any transmission experts that can give me some direction/advice.