Have a strange problem that I wanted to see if anyone had a suggestion before I pull the trans and transfer case. Recently purchased a 94 GMCc2500 4wd with the 6.5 diesel engine. The problem occurs when I put it in reverse it moves but is slipping. If I shift to 4 wheel low it works fine. It also seems to have an issue when shifting from 2nd to 3rd and 3rd to 4th. It does shift but winds out a little before it does shift. If it wasnt for the fact that it works in low gear I would have already pulled the tran but just wondering if it could be anything fixable without having to pull. I believe it is the 4l80e.Any help would be great, Thnaks