I've recently bought a new WRX. I've noticed some strange behaviour when under heavy acceleration. For example, sitting in 5th gear on the highway, travelling at just under 100km/h (around 3000rpm), I put the foot down to accelerate and overtake. The car does accelerate, but the rpm increase is what worries me. It seems to rev up faster than it should (i think to around 3700) and then drop back (say 3500) and continue on a steady climb. The car accelerates throughout this process. Is this clutch slippage or something else? I mostly notice it in 5th gear at the 3-4000 rpm range. I have noticed it in 3rd gear once in the same rev range, but not really in any other gears.
The car has a turboback exhaust, ecutek 1.5 and tein suspension (not that I imagine this would effect it)
Any help is appreciated.