my jeep grand cherokee laredo had been doing this for a long time, it doesn't do it all the time but when it does it starts surging when you get on the throttle pretty good. also it will just lose power totally some times and you cant get it to rev over 2000. when it surges it feels like it is missing or somthing. i replaced the fuel filter, 02 sensor, and plugs. please help me oh it's a 4.0L