TH400 Performance Automatic Transmissions and Parts from PATC. PATC GM Performance Transmissions and Parts, TH400 and others. PATC builds TH400 performance transmissions in many levels. PATC is on the cutting edge of performance rear wheel drive American transmission development. We work with different manufacturers in the development of stronger parts. We have the most complete inventory of performance transmission parts for Ford, GM and Dodge than you’ll find anywhere else. Using these parts we have developed performance / heavy duty transmissions in many different levels and types. This is why three to four thousand people visit one of our performance transmission websites everyday, making PATC the number one performance transmission destination on the Internet. These websites are updated sixteen hours per day seven days a week. We don’t just sell transmissions and parts, we test them in our test vehicles on the street and at the drag strip. We have the hard to find performance transmission parts all in one place and in stock. On this Website you will find many performance / heavy duty automatic transmission parts the others don’t sell.