Why does my transmision slip when my over drive kicks in?
Slipping mean the trans is not engaging. SO you won't move anywhere. Sounds like the Overdrive band is burnt or the torque convertor is faulty. This will require disassembly of the transmission, which always means a rebuild. Is the truck worth it? Maybe find a used trans?
Have you checked your fluid levels?
yes, it is good
Looking for a Used C/K 1500 in your area?
CarGurus has 1,048 nationwide C/K 1500 listings starting at $2,000.
Search Chevrolet C/K 1500 Questions
Chevrolet C/K 1500 Experts