I can help you out with this. I do a lot of trans building for Novak Adapters. Just need a little clarification. Does it slip when in 3rd and 4th gear only? What position is the gear selector in?Anyone know what would cause a 700R4 to slip in drive and over drive only? All the other gears seem to work, it will take off ok but after it shifts to drive it slips. Its in a 89 GMC 4x4 with high miles. Is it just time for a rebuild?