PWG modules (aka. accelerator pedals) rarely go bad. the issue people are referring to is the sticky/notchy "stick-slip effect" pedal feel. It is purely mechanical and is related to the lubricant used on the pedal that causes the mechanism inside to bind when it gets hot (parked car in summer or heater on in winter) OP, you would physically feel the pedal sticking if it were to blame. Also, the EML would go to failsafe if there were any issues with the potentiometers in the pedal so I doubt that's it.
Since the condition changes with altitude, I would look to an intake leak like the DISA valve. It seems like they tend to go bad in the winter.
GT1/ISIS/MoDiC = Factory authorized diagnostic system used by BMW dealerships across the world.
NCS Expert = BMW Factory R&D programming tool available on the internet (not intended for the public and not available to the dealership network)
OEM = Genuine BMW part only available from a franchised BMW dealership.
DME = Engine Management Computer