WARNING: This page is about a different car, the 2005 GMC Yukon XL, 2005 Chevrolet Suburban, and 2005 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
Converter Ballooning
Checks
Cause
Converter Limit Valve (214)
Stuck open due to sediment or undersized bore
At High Speeds: Converter Limit Valve Feedback Orificed Cup Plug