Misfire problem

[MasonFirby]

Hey guys, my 2003 4.8l Silverado has been having some problems. First off, the fuel pump went so I replaced it with a shitty used one for cheap as well as a fuel filter. At the same time, 2 o2 sensors went and now the other 2 are. Shortly after, fuel pump went again. So I bought a new one, as well as a filter, slapped it in and took it for a drive. Ran great for 200 feet and started misfiring again. Went from p0307 to p0300 and back to p0307. So I cleaned the injectors on 5 and 7 and swapped them. Ran fine. About 70 kilometres down the road it’s misfiring with p0300 again but not as bad. Why does it keep misfiring? My mechanic said coils are good, my spark plugs are fairly new and wires should be good. Could it possibly be ground wires? Or ECM? 

[Hillwood]

You running  A/C  Delco spark plugs?

[MasonFirby]

1 minute ago, Hillwood said:

You running  A/C  Delco spark plugs?

I honestly forget what plugs I put in.. AC delco no good?