Can you elaborate on this part, I not sure if I understand you complete.

 

Just for the record my truck almost over heated with the plugged cats. Like 240* temps! Also the heat shield on my manifolds are now spotless. It burned all the dirt and road grime off of them.

 

I Would Check For Pluged Cats, Then Pull All Injectors To Make Sure One On That Side Is Pluged I Have Seen Some That Have Trash In The Injector Screen And Causes A Miis Fire Or Lean Condition

 

Maybe in the morning I'll pull the y-pipe off and check it out. Will let you guys know. Thanks!

 

What I was saying is that a lean condition can happen on just one bank due to bad/plugged injectors, incorrect tuning, pproblem with fuel delivery to that side for sure.

 

Plastics is basically what I do for a living. For plastic to reach its HDT (Heat Deflection Temp) or melt (glass transition point), is a curve on time and temperature. The higher the temp the less time it takes time it takes to melt or move. It will also do the same at much lower temps if exposed to it for extended periods.

I am not saying you are not running lean. I would think that if you were running hot enough to melt that thing from 6 inches away quickly you would have toated the motor. I'm betting that the header/motor has gotten hot enough for and extended period the plastic in the wheel well to see its HDT and has done this. Looks like it may have had a cut/crack in it which would have made it easier to happen. Not certian what the material is in these parts but probably a filled PP. HDT's for these materials depending on amount and type of filler range from 200 to 400 F.