Jeep Repair: Cold engine stumble, champion spark plugs, cherokee sport

Question
I have a 2000 Cherokee Sport with a 4.0 6. It has 85k miles on it. Recently, when started cold, it will start ok but as it warms up it begins to idle roughly. Depressing the accelerator will only bring the revs up to about 1500 then the motor acts as if it has a rev limiter. Same happens if driving it cold. As it warms (about five minutes) this problem goes away. It also seems to be getting a little bit lower mpg lately. Any ideas?

Answer
Check the spark plugs, wires, cap and rotor.  Newer 4.0L's have a coil on plug rail which elliminates the distributor cap, rotor and wires.  Obviously you don't need those if you have this set-up.  The wires, if original or MOPAR will have a date code on them.  The first 1-2 digits is the month and the last two would be the year.  Example: 11-99 would indicate that the wires were produced in November of 99 (which you might see on yours since it's a 00 year model).  These need to be replaced every 60K or so.

Don't use anything other than the cheap champion spark plugs that came in the car.  All these other plugs out there may work great in something but only Champion for you.
Doug