Have a '94 JGC (4.0L I6, FI) with 130K miles. Car was purchased new at near sea level altitude--now live in Denver, CO area at approx. 6000' altitude--One continual, nagging problem. Between 3200-3800 RPM, engine hesitates and will not accelerate ("bad actor" rpm seems to vary with temp--lower rpm threshold when warmer). Condition most noticeable when transmission downshifts while climbing hills at highway speeds--will also occur in lower gear whenever rpm reaches threshold point. Cruise Control cannot handle condition--kicks off. Can also force condition by pushing O/D override button at highway speed, which causes rpm to increase past threshold point. Did a tune up per dealer recommendation, replacing distributor cap, rotor, spark plug wires, spark plugs (intially Bosch plugs, now back to Champions--no difference), EGR, etc.--no help. Engine starts normally and runs perfectly at idle and when below threshold rpm. Dealer mechanic confirmed problem via road test--no engine codes--fuel pump pressure checked normal during test. Dealer service department seems stumped--wants to replace crank position sensor next. Any thoughts??? Possible Mass Airflow Sensor issue?