12.7 Detroit backfires and throws fireballs

Watch the video and let me know what you think please

Truck info, 2006 FL classic glider, ddec4 12.7,
It's been doing this for about 3 years now, started sometime after having Freightliner do the bull gear. Engine has had a complete inframe including a reman head, injectors, pistons, liners, bearings, oil pump. Had no effect on the problem what so ever. Turbo was replaced with the bw171702 sometime near when this started, don't remember if before or after, also don't know if that could do something like this. Jake's have been rebuilt, no effect. Cam timing was off 1 tooth, had that addressed, checked gears in the front cover, injectors pass the cutout test, no codes. I'm sure there's more I've tried that I'm forgetting, but I am completely out of ideas, any help would be very appreciated

 

A few things I should add, the truck runs perfect 90% of the time, not a single hiccup. When I had the cam timing fixed it had no effect at all, doesn't run any better or worse than before. Same with the popping and backfiring. When it starts acting up is when I hit the throttle slow after coasting, only over about 1500 rpm. And never at high

 

When it pops a little it smokes grey, sometimes I can makeit do it at idle, that's really where I can tell it's puffing grey smoke and also I don't know what this means but it smells really wired when it does it I can't really identify the smell confidentiality, doesn't really smell like burning oil or anything. To be clear tho it is not very common that it has any hiccups at idle, but occasionally if I rev it while parked it will pop and crackle at about 1500, but if I floor it it will go to redline without popping.
It starts pretty smooth no matter the temp.

 

I would think if it were the head or gasket it would have been resolved with the inframe.

The the truck was originally built as a glider by a private shop with a Detroit reman. Made it over a million miles with no issues.