especially after driving above 40mph. as it comes to a stop sign you can hear it fade out. vacuum leak? maybe this is the reason for the rough idle car has when parked with motor running in gear(drive).

It sure could be a vacuum leak. I guess from reading your posts you've ruled out everything else. To find it pinch off the vacuum hoses coming off of the intake plenum with a pair of needle nose pliers and those hoses that are on the vacuum block behind it. If you find a leaker the idle will improve, then you can trace it back until you find the leak.