P0304 code

Yes i know ,but look at the things i changed already ....what else could be causing it ??

you changed all 8 coils?

just the #4 coil pack

swap #4 coil with another one that's easy to get to,clear the light,see if the problem moves to that cylinder.if it does that coil is bad.

All coil packs are good problem stays on #4 cylinder

don't know if you have checked the compression or not,but other than hooking up to scanner with live data,copy and paste the link and read through it. Part 1 -How to Troubleshoot a Misfire (GM 4.8L, 5.3L, 6.0L) easyautodiagnostics.com/gm/4.8L-5.3L-6.0L/how-to-troubleshoot-a...