Will0997

has anyone heard of havin engine failure/ruining your engine by putting a cat back exhaust on your 5.3L without disabling the AFM? ive recently purchased a ‘15 Sierra and I went to an exhaust shop to cut the stock exhaust off at the 3rd cat and put a y-pipe with dual 2.5” pipes out the back and they told me that when it switches to the 4-cylinder mode I could ruin my engine by not having enough back pressure. Anyone able to confirm/deny this from their experience? I have a Range AFM disabler coming in the mail but it’ll take about 2 weeks to come in.