At 50k, you really should change your plugs. You'd be surprised how seemingly unrelated things in fact are related.

 

Have an '04 6 speed with with 54K and the full Miltek and I do not have a back firing issue at shifting.

 

And the winner is...

Sineo!

Bad coils and questionable spark plugs. Dealership, even though they misdiagnosed the issue and I had to go somewhere else, wouldn't replace them unless they showed to be failing. So, I had the shop replace all coils and plugs. $600 later, car is running great again. Yes, I know, learn how to wrench. Some of us just weren't meant to, trust me.

 

lol congrats.. theres no shame in payin someone to do it...yea spark plugs are one of the more easier things to do but hey..if you got the money why not