Well, we managed to kill a set of 63\'s My dad managed to kill a set of 63's this past weekend at the hammers. His truck is running 5.13's, doubler, t350 and a built 400SB with TBI on 40" Iroks. I have to say that it took a while to finally kill them because his driving style is WFO when in trouble and he finally bent the main leafs. We are going to try and go with a custom 65" long or so spring running triple wrapped main eyes to keep the axle wrap down. Hopefully that will help.