By the way, I replaced the accelerator pedal position sensor and the throttle position sensor and the Yukon with 223K miles on it drives MUCH better. No more annoying lag time between pressing the pedal and getting the power. Much more responsive. I think the pedal sensor replacement is primarily responsible for this change. I did the TPS because I got the "reduced engine power" issue, and I figured with 223K I'd go ahead and throw parts at it. Appears to have worked quite well, although time will tell about the reduced engine power.