My Cherokee has this stumbling/ backfiring problem. I’ve had the plugs, wires, crankshaft sensor, and fuel pump/filter replaced. It still has the same problems. Worse when cold and going up hills. It also stumbles on the freeway. I feel it just drop power, and then it comes back. It has 220K miles with a 4 liter. Any ideas? It’s my work vehicle and I need it daily! Thanks in advance, Greg.