2008 6.0 intermittent / random backfire

Metalbender · December 1, 2020

New member here with my first GMC truck. I've ALWAYS driven Superduties.

I've read darn near every post I could find about this problem, but can't seem to get a handle on it.

My truck is a 2008 Sierra 1500 All Terrain, 6.0, with 182,000 on it.

Bought the truck in South Dakota and drove it home to western Pennsylvania and it ran like a dream! About 3 weeks later the crap hit the fan. Stabillitrac lights, check engine lights, random misfires, backfiring thru the intake, lean burn codes both banks, O2 codes, and Fuel trim bank 1, System too lean (both banks)!
Where I think my problem is different from the other posts I've read is this thing only does this after I've driven it at least 20 minutes or more, and it doesn't matter if it's city or highway driving...and it idles smooth as glass...no ticking no nothing!
It does it, if it's in V8 or V4 mode, so I think the AFM is working properly...although the oil pressure drops to about 20psi in V4 mode.
Now it's been to a GMC dealer and they told me unless it does it while they have it. they can't pinpoint it.
Here's what I've done to it so far...
New Iridium plugs (gap verified), wires, and coil packs.
New AC Delco O2 sensors, all 4.
New injectors. (small fortune!)
New Mass Air Flow Sensor.
New air filter.
Cleaned throttle body.
Getting correct voltage at each injector.
Getting current increase at the MAF as RPM increases.
The last time I had it out, I was driving at 65mph on flat road...it did it...Stabillitrac light and CE both flashing. Took my foot of the pedal, lights went out, step back on the gas and it ran like a raped ape! ...15 min later I stopped to make a left hand turn and it did it again...this time NO LIGHTS!!! took my foot off the gas and stepped back down...no problem!!

Anybody have any input!? Sorry for the long post, just wanted to give you folks as much info as possible

Greg