Hello again. My professional research has come up with 2 possibles causing this problem. 1.worn distributor shaft bushing(s) and/ or 2. worn / loose timing chain. I will be checking for excessive play in timing chain this weekend, but since I doubt it has been replaced at 124k, I'm pretty sure that repair is in my near future. My questions are : 1. if you have replaced your timing chain, did you notice any difference in the way your truck ran after the repair? and 2. has anyone ever heard of worn distributor bushings in these engines ? Just curious if this might be a common problem. Thanks again.

 

I beleive that in our truck the distributor has nothing to do with timing.