Help don't know which way to go to fix truck!

[joesherrie12]

I've been out of commission for the past 8 months with two broken legs and a bruised spine. (Motorcycle accident ) and my son in law put his job on hold and took over my truck while I was out. Well now I'm back in the seat again and found a few problems that he didn't tell me about! This is a 871 isx with 860k . to start with I had a real rough cold idle and a knocking sound once the truck warmed up both would go away so I pulled the metering and timing accuators off and checked them front metering was 3 thou. Front timing was 5 thou. Rear metering was 7 thou. And rear timing was 6 thou.so I replaced all of them! It fixed my idle problem but the knocking sound is still there. But I noticed last night when I started the truck as soon as the relief valve on the drier went off the knocking went away! Is this the compressor? I have an air leak that I can't find the sleeper bags would be down when I start the truck could it be leaking back through the compressor? One last thing I was averaging 7.2-7.3 mpg now I get 6.3 - 6.4 seems to run rough after I shut the truck down and unload and get going again. Everything is new on the egr side was done 100k ago except Doser injector. It is time for and overhead set could this be my problem?