Title says it all. Truck had been hard starting this last week but I thought it may have been bad plugs or a bad o2 sensor (it was throwing a slow response on the upstream bank 2 sensor) was going about 75 down the hwy and kicked it out of o/d to get around a semi and I felt a significant loss of power along with a knock. At idle and low loads it sounds like a collapsed hydraulic lifter but once you put it under heavy load there's a significant knock as well. Its getting trailered home tomorrow and we're going to tear it apparatus but I've never really worked on a ohc motor before. The truck is a auto with the 4.0. Anything major I should be liking at replacing or what could the cause be? Also I'm thinking of replacing the tinny chains while I'm at it cause I feel a vibration from 2-3 k rpm that from what I understand is from the chains.