The customer was driving 55 mph when he noticed an engine-speed flare and realized that the lockup was no longer holding. There also was a growling noise when the converter tried to lock up. When the converter was cut open, there was fine black material resembling graphite on the stator assembly.
The 300mm converter has become very popular in GM units. First used in the Corvette and F-model vehicles (Firebirds and Camaros), today it is also used in most trucks, vans and SUVs. The converter is also manufactured in a 280mm version (VJCX, for example).