I have a 2000 Jeep Grand Cherokee Laredo. I have a multiple misfire problem, and it only goes to about 2500rpm and starts bucking. I also have been losing power going up hills, it creeps at 15-20mph. I have changed coil packs, head, spark plugs, computer, wires, tps sensor, camshaft sensor, cat converter is off, upstream 02sensors are disconnected. What else can this be????