LQ4 Multiple misfire

[Billett]

So I've got a bit of a puzzle going on here. The shop I had my truck tuned at had some problems during the tuning process and I'm not 100% sure they nailed down the problem. Don't get me wrong, it runs pretty well, but I had my brother check the pcm on his tech 2 yesterday and we found some codes that my torque app doesn't pick up. Emissions codes were showing, which I knew about but still tick me off. They should have been turned off by the tuner. Besides that I had an oil pressure code. Fine. I pulled the original sender for the idiot light and replaced it with a sender for my gauge.

Big problem here is that with the torque app I was seeing multiple misfire problems, but couldn't narrow it down more than that. The tech 2 lets you see which cylinders are missing and it turns out it was all of them. Huh, weird. Brand new plugs, brand new wires, coils are old but I doubt they're all bad right?

Well it seemed like MAYBE cylinder 3 was having a few more misfires so we pulled the plug and swapped it. No change. Swapped plugs and wires a few times and still nothing.

Drove it around with the tech 2 counting misfires and noticed the weirdest thing. Accelerating doesn't cause any misfires. Idling doesn't cause any misfires. Constant throttle doesn't, and neither does WOT. However the counter SKYROCKETS on almost all cylinders when you gently decel. If I take my foot off of the pedal completely, no problem, but if I ease off say from 50% throttle gradually to 10% I get all kinds of misfires.

What the hell is going on?

I thought it might be vacuum, but wouldn't I get more misfires when accelerating in that case, because it would pull more air? I have no idea at this point, but I did take a vid to show the counter, just can't get it up until later. Let me know if any of you guys have thoughts.