I would checkout the hesistation first, it maybe a failing turbo hose. These are sometimes hard to find and the sure way is to remove all the hoses and clean, inspect, and replace them one at a time. You will probably find a small hole in one of them which is causing the hesistation and the dirty throttle body at the same time. Although the hoses are not cheap from a dealer they do cost a lot less than a V8 conversion.