OK, I'm stymied. Need genius help.

[SRT4Real]

I've seen many threads with variations on this theme, but my situation is really strange.

The car mostly runs fine. Pulls strong in 3rd and 4th gear. If I try to floor it in 2nd gear, it backfires repeatedly once I hit 4500 rpm, and loses power. This only started happening with cooler weather. It's much less likely to happen when it's hot out, or if I turn off the fan mod and let the coolant temp rise to 200 (usually sits around 170 - 180).

My Aeroforce gauge shows zero knock when it happens. No CEL, no codes.

I tried replacing plugs, plug wires, coil, and cam position sensor. Also tried gapping plugs at 0.32, though 0.36 worked fine for two years.

I have Stage 3 w. toys using the stock vacuum line setup, AGP WGA, 55 mm TB, SEE, DCR oil mod, catch can, check valve, short ram, fan mod, BS assembly removed, urethane motor mounts. Been running this way for quite some time.

WOT pulls are with DAB 2, but I've also seen it happen in DAB 1. Boost levels look same as ever.

Recently installed Odyssey battery, but the problem was happening before then. Used to have a WOT box... pulled it out because I thought it was the source of the problem. No dice.

NeonDan test drove it last night, and he is puzzled, too.

So... any ideas WTF is going on??