Clutch Piston
The clutch piston in a stock transmission is cast aluminum. The cast aluminum is soft and under the high stress generated by a modified diesel, it will show wear quickly. Many transmission builders use an anodized finish in order to achieve a higher tensile strength on the aluminum surface. UT's approach uses a billet aluminum that is much stronger than cast material. (Strong enough that it actually has to be machined as if it were steel.) With this material, the entire piston is stronger and more resistant to wear. It's more expensive this way, but you get what you pay for.
UT uses a forward clutch piston design that has one square inch of additional surface area over the stock design. This provides more clamping force on the clutches. It translates into 400 additional pounds over stock at engine idle and 1,800 pounds over stock at wide open throttle. They also added an additional oil check valve to the piston. Normally, the piston has one, but UT has found that adding a second valve helps equalize pressure release.