I have a C1500 with a 4.3. Just bought it as a beater. (It's been rolled). Has a little over 140K miles. From a dead stop, you have to put it in 1st or 2nd to make it move. Once it's rolling more than about 5 mph, all shifting seems to be fine. Info I've gotten so far points to solenoid(s), but I don't know which one (s). I Hope that's all it is, because it looks like a relatively easy fix.