ok did a compression test did cap,rotor,wires,plugs ok this is what its doing at idle engine shakes driving doesnt shake get to around 50-55 starts to stumble give it more gas runs fine has power it set sense july with a 1/4 tank of gas i put fresh gas in it i changed to oil today and filter and added a bottle of engine restore seems to not shake as much as it did at first got it from a buddy of mine and i got it up on the lift and seen that someone put an after market cat on it and a muffler the exhaust out the pipe (rear) sounds like it pulsing ok now i go to floor it and the engine light starts to flash let off the gas and it stops flashing i checked the injector harness with a noid light and they are all fine getting power and all of them pulse has a dim light but when i give it a little gas they get brighter i checked the alternator and says 12.6 volts battery has 12.5 volts is this right or wrong on the alternator and battery it drives great except when u go 50-55 miles an hour it stumbles i also changed the pcv valve oh i forgot the coil pack too engine mounts are good one is brand new the other is great could it be the lifter stuck i know that dodge lifters like to stick i also hooked up the computer and it says misfire #3 cylinder but no engine light on so this is where im lost its a 1998 jeep limited with a 5.9L magnum milage is 186,000 but not sure if the engine has ever been changed or not has anyone else ever had this problem or like it please let me know any info would help thank u