I have a 06 Duramax that I have changed the high pressure pump on due to a bad internal ceramic valve in the pump and lower than expected fuel rail pressure. Before the pump took a dump the truck would intermittently go into a "limp" or "safe" mode and would not allow the rpm to go above 2250 rpm. This is in a C5500. Now, it does not want to fire off without a small shot of either but runs great until driven approximately 2 miles and then goes into the "limp" or "safe" mode once again. I have taken fuel supply lines off and pressure checked and vacuum checked all lines for any leaks and none were found. Installed a vacuum guage at fuel filter inlet and has 2 1/2 to 3 inches of vacuum when cranking. Engine can idle all day long and will still achieve full rpm range but, once driven it does its' goofy thing and goes into reduced power setting until it is shut off and started again. There are no trouble codes in the ecm and while looking at everything in datastream on my scan tool, every sensor is operating as designed. I did find the engine oil pressure sending unit (EOP) was completely out of range so, changed that and it works perfectly now. The only other strange thing that I did notice on the datastream was that it shows "PTO engine shutdown signal" as engaged or active. I can't find anything to even begin to look further into this. I do know that when the PTO switch is engaged that the engine will not run over 2250 rpm as most PTO driven items are not designed to operate above that rpm range. Datastream does show when I have the PTO switch engaged and disengaged. HELP!!!!!