2017 Sierra misfire/backfire

[Snappe_z71]

Hey guys,
New to the forum. I just dropped off my 17 at the dealer last night. Has 9100 miles on it. Has a 5.3 with the AFM. I have a cold air intake, diablosport 87 octane tune and a flow master catback exhaust as well. Couple weeks ago when I put the truck under a heavy load, for example going up a steep incline whether it’s in 8 or 4 cylinder mode it starts popping/backfiring. I can only describe the sound as a bag of popcorn popping in the microwave except it’s doing it under my truck coming from the exhaust. I checked for exhaust leaks and made sure nothing was loose or hitting anything. It will also do it on level ground as well after awhile. The backfiring is way more noticeable in 4 cylinder mode. I have no check engine light and no codes. And if I mash the gas she gets up and goes no problem. The aftermarket mods were done 5 months ago. What could this be? I came from ford trucks and this is my first GMC.

Thank you

 

[havasued]

mine too

Hello I have a 2017 sierra 5.3 and it does the same thing on light application of the throttle while in 8 cyl mode or 4cyl mode at any speed even when in cruise control

 

[98trck]

I wonder could the O2 sensed be sending incorrect measurements to the ECM
try unplugging and plugging in each O2 sensor maybe there is not a good connection and doing this may help

PETE