I was helping guy work on the 2007 gmc Denali 6.2. Loss power when drive engine light flashing then off. And come back. I scanned and it show p0300. I did feel rough idle. So I replaced all spark plugs. Still doing same. So I cleaned throttle body, replace map sensor. Still doing same. Replace old battery and I ran each coils pack and spark tester light. All of them 8 are good. Checked all wiring looses to be sure it all tight. Still same proble. Do you have expericne this before with your vechiles? Hope hear from you.

 

would you say the misfire starts as rpms increase? how does it idle?
if sitting in idle and you quickly floor it, does it "bog down" at all or sound weird?

 

Idle rough. Have to rev to 1500-2000 rpm it smooth. When you drive it shitty

 

Hmmm I'd almost check the cats. Could be plugged.
With your scan tool.can you check the short term andlong term fuel trim percentage?