99 Yukon 4x4 - Vibration Problem

I have a 99 Yukon 4x4. It started out if I was driving up a fairly steep hill above 45mph the front end would start shaking. If I was pulling something down the highway the front end would shake and it would seem to move through the vehicle. This would continue intermittently. I never found out what the problem was but over time something has gotten worse. It shakes all the time now - really bad over 65mph. I don't know if it is related. My SES light came on and the code said there was a miss fire in #4. It has 97,000 miles. I replaced spark plugs, plug wires, rotor button, distributor cap and the SES light still says miss fire on #4. I had spoken with another 99Yukon owner a year ago and he said that his shook like that too. Does anyone know what this shaking is? Is this possbily related to the miss fire on #4 or is this possibly something else? Any help would be greatly appreciated.



:banghead:

Check the steering parts for loose. Most likely the idler arm.