[Tom Goldman]

Yes Bob , I know your car.
Without data like driveshaft rpm or throttle stop rpm ,its sometimes difficult to pin inconsistencies on any one thing ,so the tires usually are suspect when they have a large number of runs on them.
Since the problem started with the converter change ,I would suspect that it's probably hitting the tire harder than in the past. ......A bar position change or a much stiffer shock setting than was used in the past may be needed. maybe even different tire pressure .
come by and see me at the NED points race in a few weeks and we can talk.