Bringing this back with a solution that worked for my 09 SS/TC (GMS1, hahn catless downpipe, k & n intake, zzp front mount and hard charge piping) and a friends 08 SS/TC with a similar setup.

Both of us had an issue with missfires during WOT and usually in second or third gear in the 3500 to 5500 rpm range.

If you don't have dielectric grease bewteen each coil and the spark plug....do so (also use it on the coil wiring connections)...I also added a ground from the passenger side of the cylinder head to the strut tower. Coils are grounded to the opposite side of the head but this will help as most GM owners in general know they are horrible for ground issues

Try this before you do anything else of a higher $$$$

Just my two cents.