Car occasionally loses all power when driving, misfiring, -25% and +25% fuel trim

[dvdbck]

Car is a 2000 Boxster S, with a 3.4 engine and ecu from a 2001 Carrera. Electronic throttle control.

I changed my o2 sensors a month ago, it solved the misfiring issues I had been having. Car has been driving perfectly until a couple days ago.

Out of nowhere, my car lost all power, shifted it to neutral, would not build any RPM with any throttle, and had noticeable vibrations. By shutting the car off and turning it back on, it returns to normal function.

The car has been stuttering, like low power or misfiring, as I build rpm through 2500. Its accompanied by occasional flashing CEL and codes for misfiring cylinders 4,5,6.

I have cleaned my MAF, swapped my o2 sensors around, reinstalled an old one, tried to find any obvious air leaks past the MAF. Nothing. I used an OBD tool and found my short term fuel trim for bank 1 is -25% at idle, and with rpm it goes to 0. Originally my short term fuel trim for bank 2 was looking normal around +/- 1%, but after messing with the o2 sensors it is at 25% following a short test drive.

I don't know if its related, but while cruising a week ago I heard a "POP" noise, didn't think it came my car but instead came from the road, but there are no such things as coincidences.

Any ideas?