2006 express 4.3 1500 4 speed auto trans. 1 and 2 are fine. 3 and Drive slip bad. Happened all at once. When parked all was well. Next morning I start-up and the shifting problems happens. Thanks in advance for any help. tom

 

Sounds like a rebuild.
I lost 1st gear on my 90 van with a turbo 350 tranny. I was still able to drive in second and drive, but it was a rebuild to fix. I would not mess with it and have a tranny shop take over.