I have a 97 gmc with a 5.7 vortec has 200k miles new plugs, wires, idle air control valve, throttle positioning sensor, ofc valve and boots, and fuel filter. When idling it sits at 1100 to 1400 rpm. Idle is adjusted down all the way and timing is on, but still idles high. Lot of vacuum coming from valve cover when pulling oil fill cap. Also at times acts like it has a misfire when getting on the throttle hard (hence the new filter and tps) but still doing it only when motor is grunting hard and no misfire codes. Just started about a week ago. Next thought is intake gasket (haven't tested) just seeing if anyone has had the same issue and what caused it and also how ling it takes to replace upper and lower intake gaskets on the 5.7. Normally a ford guy but got a smoking deal on this gmc so not up to snuff on GM motors yet.