backfiring through intake/power loss

I have an 89 XJ 4.0 auto 4wd. The problem i'm having is a longer cranking time before start and backfiring through intake with loss of power. once started it will idle and rev fine but when I drive it takes off fine but once at a steady cruising speed for a couple of seconds it will drop a couple hundred rpms and act like its loading up. If I try to accelerate thats when it backfires. But if I floor it downshifts and runs fine. I can also make it do it by holding the brake and giving it gas. I have a new fuel pump, fuel filter, tps, cps, cap rotor, air filter. any help would be apreciated. I just got this jeep about a month ago and am starting to get discouraged.

I would first make sure the firing order is correct. A few days ago, I got the no.3 and no.2 wires switched, it still started, but it backfired out the intake and I lost power. Maybe a sensor is failing?

it sounds like a bad oxygen sensor, that is if your 89 has one. my 91 did a similar thing when the O2 sensor was toast

Timing or running lean...

I would check your spark plugs and make sure their gapped properly... Wire order or timing as well, have you taken out the distributor lately?

I checked plugs and they need replacing. going to change them tonight going to change the wires just to make sure there not a problem.