I had a similar problem with my 1992 model. It is an automatic extended cab. Have you checked the linkages underneath the truck on the transmission? I found that the plastic guides for the metal linkage rods were brittle and falling apart. One was already completely gone. I had to go to advance auto parts to the HELP parts section and find some new pieces that I could make work. Just a suggestion. This fixed the problem with mine. It was doing the same thing.