1996 suburban 350 vortec engine is missing.

[jimmydude]

This thing is giving me fits. It has a miss at idle and also when under load like pulling 4000 lbs trailer. It runs fair around town, but I can feel a slight miss all of the time. It also sometimes shakes at idle and nearly stalls. I put new wires, cap and rotor, plugs, egr valve. I had it put on a scan machine the guy said it has a bad valve guide on number 4 cylinder. ( I think he is nuts) That is where the miss is I guess. The plugs looked good when I changed them out. Compression test is within 5 psi on all cylinders. (150-155 Lbs) This engine has 207,000 miles on it and has never been torn down for any repair. This thing uses a little bit of oil but no big cloud of smoke at start up. Could it be the timing chain? I had a friend watch the rotor as I turned the crank shaft with a wrench, we guess that is has about 12° of play in the crank before the rotor begins to turn. Any suggestions will be great. Thanks, Jimmydude