There's a plate on the cam gear (Behind the front timing cover) that the cam position sensor pulses off of to get the cam position. These are bolted to the cam gear and will not just come out of timing. Everything that controls the Duramax is electronically controlled (I.E Main Injection Timing has 3 tables build into the trucks programming that is referenced off of fuel flow, RPM and Barometric Pressure.) Its not something that will just come out of adjustment all of a sudden. I have a VERY good dealer that builds duramax's for competition use that can probably diagnose this for you. If you are in the Ohio area still, He is in Urbana. Unfortunately something like this will require the GM TechII Scan tool to see the live computer data to determine why its not starting.
My initial thought on all this would be that since its "Makng Oil" and having a VERY hard time starting, there is a high pressure fuel leak and is bleeding off rail pressure into the valve cover. This has come up a few times in the past month and is probably worth looking into. A lot of times i see older LB7 Duramax's like yours build up some junk on the seat that seals the high pressure fuel line to the injector. When injectors get replaced, this seat is completely overlooked and not cleaned before it is reinstalled. If this is the case, the fuel being pressurized by the pump will bleed out into the valve cover (which is where the injectors are located) and will let the fuel mix with the engine oil. This will also cause a no start scenerio being that the duramax's need a MINIMUM of 3600PSI to even start. If there is a leak like this, the pressure will not be there to allow it to start.
2003 GMC Sierra LB7 New motor in the works as we speak with lots of goodies!!!