I have a 1989 3/4 ton 4x4 suburban that had lost 3rd gear but now it is working. The issue started on a rainy night on my way home from work. I hit a big puddle and the vacuum line on the vacuum modulator popped off. I put it back on but for a few days after that it would kick down under mild acceleration. I then changed the modulator and it seemed to fix the problem for a few days. Then it kicked down again a few times like before I had changed the modulator. Then it lost 3rd gear and the pump(?) started to make noise (it almost sounded like gear drive timing). I stopped driving it and parked it for a week. Since then I have moved it around my yard a few times but never enough for it to get out of 2nd gear, but it was still making the noise. Here where the story gets odd I took it for a trip down the road today and it shifted fine and no more noise. I picked up some fluid and a filter before I changed the modulator but have not changed it yet. So I think I am going to run some trans flush through it and change the fluid and filter and start to drive it again. Anyone have any ideas on what happened or what would cause this?