Hi,
Coils are a know problem, but would cause a missfire rather than loss of power.
would be worth checking your MAF sensor ( only buy genuine vw exchange units ), coolant temp sender and e.c.u power relay ( if fitted - some did some did not ). or could be fuel filter, all of these are common and could cause running problems so worth getting them all checked out.
Hope you get to the bottom of it
Jochen.