What's inside these trannies that makes them so strong? Well, unfortunately, it's proprietary information that Thompson isn't comfortable with us publishing. But it sounds like additional clutches are added to manage the torque without the need for increasing transmission line pressure above stock. Thompson did assure us that every one of the upgrades developed for his 4R100 and E4OD comes from tearing down smoked trannies and strengthening whatever failed. Every transmission he builds is stronger than the last one because people are pushing the Power Stroke engine further (now well over 1,000 lb-ft!) every day. We'll take his word for it because he backs these babies up with a two-year warranty--even in trucks like ours.