i had a very similar issue in mine, but all of a sudden it just stopped.
Is it like, the car runs completely fine for first 5 minutes, then it kind of feels like the car weighs 3 tonnes and the engine is struggling to pull the car?

__________________
STi Ver 6 | 2.1L Stroker | 418whp | 11.5 @ 199kph |

Not fast enough dammit!