5.4 misfire low RPM's on freeway
This is what has been happening lately, and im not sure what exactly is wrong with it. I just dont want to keep throwing money at a bunch of different parts when it doesnt fix the problem. Once my truck warms up and I am either on the freeway or a back road (anything above 45 mph) my truck will start to shake and stutter (misfire). It will continue to shake and shutter until I step on the gas a little bit and get the RPM's up. I have replaced the fuel filter a few times, and the plugs too many times too count. Everytime that ive replaced the plugs, it'll run fine for a little while then it'll go right back to what it was doing just after a couple months. The last couple times Ive done the plugs i noticed that the tips were a little white, which means its running lean if im not mistaken. My trucks got 165k on it, and as far as i know the O2 sensors have never been replaced. Also my friend told me that the "cats" are known to go bad on my truck, and those are also stock. And I do have an upgraded exhaust on my truck. PLEASE any help or comments would be GREATLY appreciated, I am so frustrated.