I have a 2002 Civic LX with an automatic tranny. Last year I had the transmission fluid changed at the dealership even though it was working fine. It was a suggested procedure for that particular mileage. Since then, when trying to change out of first gear, the tach indicates that it has to get between 3 and 4K revs, before it shifts. The dealership mechanic had no explanation for this. Any ideas what happened?