I developed an intermittent knock about 3 months ago that would come and go...Now when the truck is cold I'll start it up and it runs for about 45 seconds and starts knocking very loud. Then after it warms up it goes away, but then going down the road 2k rpm and up I can hear it a little bit. And it smokes a little bit at idle and a little worse with it in gear and the a/c on. No drop in oil pressure(mech gauge), no fluxuation in boost pressure...last motor I had in it smoked at idle it was a worn rocker arm so I'm thinking valve train problem. Anything else I should look for before I tear into this beast again? Opinions? (Motor is a '93)