My GC used to slip gear when the engine would warm up. I brought it to the dealer for a fluid and filter change. It took them 4 hours and cost me $275 and it didn't help the problem. I brought it to local mechanic and he discovered that 2 of the bolts on the transmission housing had worked loose and that the transmission was actually starting to pull away from the engine. He tightened them up and it's been fine ever since. It's worth checking. My experience is that most of the GC problems are silly problems like loose wire harnesses and bolts rather than expensive sensors and computers.