I have a 2001 Silverado 5.3 with longtubes and and 93 octane tune. Recently my service engine soon light started flashing and read cylinder 2 misfire. So I checked switched coils and wires and it still misfired. I switched the number 2 and number 4 plugs and then it read cylinder 4 misfire. Right now I have the ac Delco plugs in them my question is should I switch to another plug with those mods or stick to original and just change em out evert 20k miles?

 

Ngk 4177 tr6

 

With those mods you would be fine running OE plugs. When was the last time you changed plugs and wires?

 

If it's got more than 100k on the odometer, switch to copper plugs. NGK TR5 would be fine, or TR55 if in a hot climate.

Copper plugs do considerably better in a engine that may get more oil in the combustion chamber than when it was new. Iridium/Platinum plugs will foul out faster.

 

I use NGK TR55's

 

I used NGK TR55 gapped at .055" when I was naturally aspirated and she ran great.