1988 Jeep Cherokee Idles ok, but misfires totally if gas is

4.0L engine, have checked air, gas, and spark and all look good. Engine will idle ok, but seems to misfire completely once throttle is applied, with complete absence of power.

Plugs and distributor cap & rotor are fine and spark checks out ok on all 6 wires. Fuel pressure at fuel rail is right on spec with fuel pressure meter. New fuel filter also. Exhaust has been tried with muffler/catalytic removed. Catalytic was clear. Airbox is clear and air filter is new. No vacuum leaks that I can see.

Tried to check trottle position sensor, but was unable to get a reading. Can this sensor or some other sensor be causing this?

This problem started being intermittent at first, and would usually start once the car first got warmed up, then would settle down after misfiring for a minute or two. Now it messes up all the time.

Another question - how much play in the rotor (side to side) is ok? There is about 5-10 degrees of play when I checked the cap/rotor.

Other things I've thought about are fuel injection system or worn out timing chain.