[Mike Kast]

have you done the propane around the intake manifold while running test yet? They caused me more crazy ghost chasing hours than I can say. Those things might last a couple of years or so but they always seem to fail slowly, minor adjustments resolve issue and then majorly, nothing resolves issue. Much head scratching and denial ensues...
while running, send some propane around the intakes and the airbox, if the idle goes up you have a vacuum problem. Partial engine drop required and while your in there...