High idle

94 Pontiac trans sport 3800. Started weeks ago, idles very high in neutral and park up between 2500 - 3500 rpms never over 1000 in drive and reverse. I have replaced upper Plenum, idle air control valve, throttle position sensor, mass air flow sensor, and the computer. The fuel pressure is right on, new tune up

parts, I also put a new egr valve on. The smoke test at the shop shows no vacuum leaks. Today I also put the 140 amp alternator on because it previously had the 105 amp which was wrong. I still get high idle what's next. P.S. Cooling system is great and I put new temp sensor in today. There is no check engine light.