I've got an '09 S3 with MTM remap and turbo-back exhaust. The mod's were done years ago and have given no issues. However, I just noticed an odd loss of power around 3500 rpm. If I floor it, the engine accelerates up to around that point, then hesitates like I took my foot off (can actually see the rev counter drop briefly back), it then recovers and accelerates ok past that point. This is most noticeable in high gears where the revs build more slowly. I can't imagine that I wouldn't have noticed this before. No recent changes to the car, although just filled up with new flavour Shell VPower. Suspecting some engine or management system issue. Any ideas?