Wow JFD444! I thought mine was for sure a unique situation. My 99 gmc suburban is doing the same exact thing. I'm a seasoned auto tech so it is truly driving me bananas, especially since my truck is in superb shape and runs perfectly otherwise... not to mention we are in a blizzard and getting 18-24 in of snow (I'm limited to short trips only). I did some trans rebuilding in tech school and was always one of the best students (according to the instructors). I'm gonna replace shift solenoid A and see what happens. I suspect it is losing power thru the coil field windings once it heats up or just plain old binding up. After all it is just an electrical part. I'll post results.