6.0L Problems.

[Wet..Paint]

So I have a 2003 GMC 2500HD with the 6.0L. This thing has been a damn lemon from the time I got it. Started out with an intermittent no crank, which I had to fix cause I needed the truck, it was the ignition switch / wiring. The not so major issues I am having off and on currently are intermittent service brake light, and intermittent service 4wd light. Of course neither of those will stay on or come back when I have time to try and scan it or stop at a shop...

Now the serious stuff... Had a check engine light come on about 2 months ago, scanned it and I need knock sensors, well work was busy so couldn't do it, couple weeks later it starts running HORRIBLE! Sounds like a lumpy cam on idle, stalls out in the cold etc. Scanned again, has like 8 codes... Knock sensors, couple misfires, lean condition both sides, Maf or Map? Sensor, O2 sensors.. Whatever, it was eating fuel had no power and ran ****ty, but being my tow machine I had to drive an hour on the highway so I rocked it anyways, got back to the City stop and throw gas in it, start it back up, no oil pressure! Of course me being me I said **** you truck and drove it home anyways (20 min drive) it made it so I left it on the driveway for 2-3 weeks... Had to pick something up so i fired er up again, has good oil pressure, so I drove it for that week, parked it again for a week. Start it up today has good oil pressure drive around, stop for gas again, no oil pressure again! Me being me again I drove the ***** home haha (20 min)

Where should I start? I think my plan is compression test it, if thats good, mech oil pressure test. (where can I hook up?) good or bad I will go from there.. I don't want to throw money at this thing if the motor is ****ed I'd rather swap a Cummins or D-max in it. (Before we all say no, I'm an ex Diesel Performance Tech) Just not sure about this damn 6.0L if its worth fixing or what....

*Drinks a beer or 3*