What size is the catback? When and exhaust is undersized, you can get the 'blowing' sound you are describing due to the excessively high velocity thru the small diameter pipe.

 

3in is the new mbrp

 

What type of muffler does MBRP use in that kit?

 

When my truck was bone dick stock I threw a cherry bomb glass pack right after the cats and just left it open for fun. I had a very similar issue with it sounding like an air pump @ WOT..

 

True I had similar issue when I got mine was exhaust pipe to small went to 3 inch fixed my problem now my intake sounds like its gonna suck in the fender. Just need to ip size of pipe after muffler

 

the MBRP has 3in pipe. but if its like the old setups iv had back in the day its just he y pipe and cats. its a blow thro. muffler with the kit. but im going to try a diff muffler i guess. just didnt know it any of you guys had this as well.

 

Pretty sure all 6.2L came with 3.5" stock. Mine did. If so, you actually just DOWNSIZED your catback system.

 

I got the truck from a friend that needed help and he had exhaust on the truck but didnt save the stock so he put on stock 5.3 exhaust. So I went to MBRP. Wanted to try somthing diff. Other then corsa, so Tryed this. Wish I would have when with what I knew or 4in duramax like I had a few years back. Would love to find stock exhaust if u know anyone! Lol

 

I have my stock catback. Shipping a full (uncut) exhaust from Salt Lake City (84118) to North Carolina probably aint cheap though. Let me know if you are interested.

 

I would take it an exhaust shop and have them go from the Y back with new piping of the correct size, get a correct size muffler. Just dump it before the axle to save money