The old thrasher kits were made by transgo and where a selective firmness performance kit. The current Transgo SK4T65E production kit is NOT a performance kit and shouldnt be confused as one though it shares many of the same parts that the thrasher kits used. Installing a transgo kit is not going to really firm up shifts much so if that is your intentions it is not the way to go. I uses the transgo kits in all of my builds but I also do some internal work to get the shift firmness where I want it which isnt feasable to most DIY guys wanting a quick install as it would require tearing most of the trans apart. The Intense shift kit is probably the most complete kit with selectability. It costs the most but again is the most complete and probably the best route to go if you cant find an older thrasher kit.
