06 AWD SS, ignition coils 5 and 7 were not firing correctly. A friend had a meter that links with the frequency of the coils. 5 and 7 had a very rapid frequency. I changed both coils and the truck came back from the dead. Full power, no hesitation and what felt like a misfire was gone. This has not thrown a light or a misfire code. About an hour into putting some miles on her the same issue came back, same 2 coils. Any advice?