TRE recommends the factory synchros from Mitsubishi. TRE has been using them for years and we’ve been modifying the blocking stops for the synchros and engagement teeth on both the gears and sleeves for over 25 years, it’s old news. 

FYI: Did you know that the old fiber lined synchros from Mitsubishi actually have a higher friction coefficient than the “bronze” synchros? It’s a fact. However when driving hard for extended periods of time these high friction synchros would cause the steel cone to overheat and smear the metal, which lead to terrible shifting.  Carbon fiber lines synchros are also guilty of overheated the cone.