i understand the concept of the tranny not meant for huge powerI wouldn't depend on someone else's success with this trans, they could be one hit wonders and that doesn't mean your w58 will hold up the same. The R154 is considered WAY tougher and beefier than the w58, and yet many people have grenaded R154's at 600hp. w58's were designed for GE motors. In the eyes of toyota, GE motors aren't supposed to put out major hp like the GTE's so they put in a transmission that would match that relatively low amount of torque. You can try to take your w58 above 400whp, but I can almost guarantee you that it will pop. If your goal is no more than 500-600wtq, I say swap an R154 in. If you plan on making more torque, then the V160 is your only option as far as manual transmissions go, but that will mean you'll also need a 6spd rear end. Just go with an R154.
From what I've been reading when you start reaching past 400whp:i understand the concept of the tranny not meant for huge power
im running over 500hp right now on it
im trying to see what is the main cause of the break
when it broke...etc
a highway pull shouldnt do it because theres not a lot of stress on the tranny