Engine Performance problem
1991 Jeep Comanche 4 cyl Four Wheel Drive Manual

"The symptoms: mid-range problem, engine jumps, bucks, cuts out, won’t accelerate, occasional popping. If I baby it and just go real easy on the throttle, even lugging the engine a little as I shift gears, I can get it to gradually run all... the way up to highway speed without it missing a beat. But, if I push the throttle into mid-range, it does all of the above, in any gear. Or, if I stomp the gas peddle tight to the floor and hold it there, the engine levels out and will accelerate, until I ease off to mid range again, and it immediately starts acting up. Barely runs at mid range throttle. Once at highway speed, it will cruise smoothly with no problem, until I push the pedal to mid range.

"New parts installed so far:
Treated with fuel injector cleaner
Fuel Filter
Crankshaft Position Sensor
Throttle Position Sensor
...Spark Plugs
Spark Plug Wires
Distributor Cap
Distributor Rotor
Ignition Coil