Suspect

98 XJ sport 4.0
Been having an intermittent high idle issue for several months that has progressed to almost constant erratic high idle and more recently a slight to severe (enough to stall at times) stumble when the throttle is applied. These two symptoms seem to accompany each other and worst on cold start and gradually improves as the engine comes to operating temperature but not completely alleviated usually. The stumble occurs as soon as the pedal is pushed even if only slightly and is overcome nearly immediately. With a computer reset, the problems dissappear and gradually return, typically within a day of driving and get progressively worse from there. I have an occasional transmission solenoid circuit code, more recently I have gotten an occasional emissions code. Within the last month or so I have replaced TPS, IAC, MAP, IAT, ECT, upstream 0², battery, and plugs. I have cleaned the throttle body several times including the IAC pintle seat. Fuel pressure is 48 psi running, although I can't remember numbers for the leak down, it was within spec per the book. I have cleaned every ground I could find. Vacuum is around 15hg. I smoked the intake (just with cigarette smoke through a vacuum line and could see nothing but a small amount from the butterfly shaft bushing which i assume the map should account for. Exhaust restriction vacuum check looked good. Distributor terminals cleaned, very little play in Distributor shaft. Spark is verified. Unplugged the clock switch without change. WTF am I missing? ECT 5V reference has 5 volts unplugged and ≈2.5 when plugged in. Is that normal? Could there be an issue with the TCM and the 5v reference sensors?