Lean Idle only when pressing brake pedal

[AaronAutoCS]

Got an oddball issue, but fortunately not completely crippling as the vehicle can still be driven, it just threatens to die-

Park/Neutral/Reverse have no problems, but when you're in drive (wheels chocked/safety first) and you press the brake pedal, fuel immediately runs from 14.7 to 17-18+ on the lean side. AC can be on or off, same problem.

I've played with adding a bit to the maf/ve table, no change, revert
same with the idle/rpm tab functions, higher and lower, same issue.
Checked torque management to make sure it wasn't doing something odd, no dice.

Anyone seen this issue in the wild? Log is idle/wheels blocked/drive/ac on and when you see it go lean, that's just me hitting the brake pedal.

OH- also disconnected the brake booster and tried the same thing- no change! (I thought it could be a leaking booster, but no dice again)

Help

2000 Chevrolet Silverado 6.2 221.233.hpl6.2Ghost4L80;4.10;Knockoff.hpt

[gametech]

That is odd. When you think it is going lean, it is just bank 1. Bank 2 is going rich at the same time. This coincides precisely with the computer going into open loop, and goes back to normal exactly when it goes back to closed loop. Is this a new build?

[AaronAutoCS]

Build has 4K miles/4 months on it so far, mechanically no issues found, did an amp clamp/oscilliscope test on the starter, no real variation in cylinder to cylinder compression-

injector drop test was within 2psi across all 8 injectors, smoke test showed no leaks. I'm truly stumped.

I have a suspicion that the pcm is going bad though, and here's why- knock sensors work (verified with oscilliscope) but it still gets the low voltage knock sensor codes, which is why they are turned off did a wire trace from sensor to pcm connector and verified it could handle a 5v/3 amp load, so whatever translates the ac knock output inside the pcm is not working.

[gametech]

I would write entire a new file to the pcm before calling it bad. It does not happen often, but I have seen some odd behavior that was cleared up by writing over what must have been a bad software download.

[abc]

What's the alternator doing when you press the brake pedal? I'm wondering how much load is being placed on the electrical system when you replicate this problem. It is interesting what the NBO2's do when the issue occurs. I would look into everything that gets activated when the brake switch is applied.

[gametech]

We really need injector bank2 pulsewidth added to the log to verify that it is the same as bank 1 when it goes open loop and the narrowbands show the opposite readings from each other.