I replaced both heads on a 5.7 and it ran fine for a while. Now I noticed soot on all the right hand side plugs and also coming out of the exhaust. I already checked the PCV and the EGR is new. New oxygen sensors as well. I got the P0151 code but once I cleared it, it never came back. I'm kind of lost and the dealership ripped me off too many times for me to trust them unfortunately. Any ideas?