Hey, I did some searching but couldnt find the answer i was looking for. I am looking at some MBPR exhausts and have AFM on my 5.3L 1500. How does it sound when it kicks into 4 cyl mode? Is it really bad or noticable at highway cruising speeds? Thanks for the help.

 

I had the same question. I just recently installed a Magnaflow muffler in an otherwise stock system. It is not very loud at cruise (at least in the cab) so the change to 4cyl is not noticeable at all. I don't know if there would be an issue with a louder system or not.

 

I added a GM Performance Touring Exhaust system to my 08 Sierra 5.3 with AFM.
You dont hear anything when stepping down into 4 cyl mode, but hear a slight pop/oomph type sound when kicking back into V8 mode- not very noticable, especially if you have the radio on. At times I drive with the stereo off just to hear it.