Hey all, my 03 3.4 Monte is having a classic case of backfiring just about anytime I'm over 3k RPM, as well as a small jump in torque when at part throttle passing through 2600 RPM. It's been 4000 miles since my head gasket job and I've been working out little hiccups since I did the job. The car ran tip-top for a few weeks after the job so I think something has worn down or come loose, all help is appreciated, thanks in advance. I have a video to post as soon as I figure out how lol.

 

Here are some videos of the problems I'm having.

RPM jump:

Afterfires:

 

The second video looks like the transmission slipping to me

 

That wouldn't cause the afterfires though, would it?

 

I forgot to mention that I've seen up to 12 degrees of knock retard during these afterfire events.