I agree with you that diagnostic fees are legitimate, and should be charged if one doesn't have the work performed at that location. His explanation of why we were not charged 3 months ago and were charged now doesn't fly though.
I don't know if the car runs well now or not. My closing statement to him was that we we're getting rid of the car, that I'd never purchase another GM vehicle and that I'd never deal with his dealership again. The new Toyota runs just fine though
BTW - We had problems with this car dating back to when we had the first 3,000 mile maintenance. The lower manifold gasket problem that we recently experienced is a documented issue with that year Impala, and there was a class action suit that GM lost. Unfortunately for us, that was the old GM, before they went into bankruptcy. A shame, because the car only had 50,000 miles on it.