My truck only has slight power modifications, TST #12 (97 5 speed). I have had a South Bend Rally clutch in it for the last 100,000 miles without any problems. It's about time for a new one, so I started looking at SB's site. To my surprise, it lists the Rally clutch as "not for heavy towing". I don't remember seeing this note when I purchased the first Rally clutch about five years ago. With the current Rally I have regularly towed 10k and 12k loads across the country. (never went over my 20k gcwr of the truck) I wonder if the design has changed?