Mine is doing something similar - 2003 GMC 1500 Z71 w/ 5.3. It has 78,000, I am the original owner, and I have changed the tranny fluid every 30,000 with a filter. Fluid is full and smells fine. When going up a two lane road at around 50 MPH, running around 1500 RPM, very light throttle, it seems to jump in and out of 3rd to 4th then back again, all under steady throttle on level ground. Shifts back and forth, back and forth. Can't tell if its the Torque converter or what. Someone suggested it might be the TPS. It may be, but has anyone else experienced this? Just would like a second opinion before I start with a new TPS. Thanks.
