I just replaced the lifters on the drivers side. When I start it I get code 0300. Multiple random misfire. When the rpms are brought upto 1500 it cleares and runs smooth. It vacuum leek. I think. Any advice?

 

Does it actually seam like it is misfiring? Can you feel it?

Reason I ask it because my 5.3 was giving me the same code but I could never feel it misfiring even though the shop scan tool would show the misfire. Shop rebooted the computer and made it relearn and the "misfire" was gone.

 

What year model is the truck? I would check vacuum first, it's easy and cheapest. Next would be to make sure coil packs are secure and double check your firing order(although this should be noticeable at any rpm). Have the Ignition Control Module tested at autozone or another store like it, AZ does it for free. Next would check vacuum coming from Fuel pressure regulator. If fuel is in the vacuum line the regulator has failed.