Big block 496

Hello I have a 2001 2500hd with a 8.1 And I have been have a long crank issue and sometimes I have to put my foot on the gas and it would start and run rough and clear up and I found out it had the wrong year cam sensor In it so I put the correct one in and ran the relearn for cam and crank and it ran the best it has in a long time so I take it for a drive and I park it to get up the next morning to take it to town and it won't start up again so back to light pressure on the gas and it fired up to having a po300 random misfires runs like crap so I started with plugs /wires and even swap out a old coil with new one still misfires on cylinder so I check fuel pressure and it's at 55psi when idleing and I pulled off regulator to see if it was leaking and nothing and of corse fuel pressure jumped up like its suppose to so I figure maybe fuel filter so I put a new one on and the same thing still so then I have it running and I just unplug the mass air flow to see if it levels out and nothing. So if anyone has experienced this or has any idea what's wrong please help me. Thankyou!!!

cleveland63b

do you have access to a scantool?

Big block 496

Yes I have a the brick Snapon scanner.

Big block 496

I had misfires on all cylinders and I have changed the crank sensor and relearned it to see if that was the issue and it still acts the same way but the cylinder have cleared up only misfires I have now are on cylinders 1,3,8 and I checked fuel pressure it's good and I also swapped injector from a non missing cylinder to number 3 too see if it was a bad injector and it still missed on that cylinder 3 so I swapped coil and nothing and different plug, and different plug wire and still the same I put a noid light on the injector connector and it flashes so my next step was too disconnect the o2 sensor one at a time and see if it straighten out and nothing so my next step after that is to get a vaccum gauge and check vaccum with it running and see what it has.