3800 RPM Bogging and Backfire

Vehicle, 1987 Cherokee, 4.0 AWD, Automatic. After receiving a new flexplate, torque converter and a used auto transmission I now have bogging/cutting out with occasional momentary cloud of black smoke from the tailpipe along with backfiring in the exhaust. If I try to go faster, engine acts like it will die. When engine is cold it misses at all speeds which partially goes away when warm. Engine used to feel powerful, now it feels like a slug. Same tires and gear ratio as before.

At highway speeds it is impossible to pass or move thru traffic. Off road I can lock down to 1st/2nd gear and the same thing happens at 3600 to 3800 rpm. Won't happen with load only, 3600-3800 rpm seems to be the magic spot.

The engine was overhauled 40k ago and was running fine. CR is 140,150,150,150,150,150.
In the last year I have replaced Battery, EGR Solinoid, Cat converter, muffler, ex pipes, 02 sensor (44K), fuel filter (twice), fuel pump, fuel pump relay, coil, control module, distributor, dis cap,rotor, plugs Champ copper plus, plug wires, no leaks at intake/ex manifold, CPS, FI Coolant sensor, knock sensor, map sensor, mat sensor, TPS and adjusted to specs, blocked off vac lines to heater/ac from engine, blocked off EGR Valve (for testing).

Still have original Fuel Injectors and they are not leaking. Spark plugs are black sooty not oily.

Today I verified that the shop used the correct flex plate.

Took it to a local Jeep dealer, who claimed to have replaced a vac line. Jeep did not throw a computer code.

Suggestions/help/advice?
Thanks in advance
Mike, Nashville

Coolant Temperature Sensor

Replaced the coolant temperature sensor, ORiley, lifetime, has 5K miles on it.
Thanks, Mike

Having done a flex plate replacement, I remember that I had to disconnect the exhaust down pipe from the manifold. That's right where the O2 sensor is located. Some of the symptoms you describe sound to me like they are fuel delivery related, and the O2 sensor is part of that system. It is possible that the sensor or the wiring got damaged with all the messing around to replace the flex plate and tranny.

Check that. Also check the CPS -- it mounts in the bell housing and it, too, could have been damaged, or perhaps not reinstalled correctly. The right bolts for the CPS have a shoulder. If the shop lost those and used regular bolts that are threaded full length, the CPS might be just slightly out of position.