3rd is geared about 50% more than 2nd, so give than a reasonable condition saph/3door will happily take more than 300lbft in 2nd, there is no reason at all that 500lbft should break traction in 3rd unless there is something up with your tyres etc, especially given that the 3 door has more grip in 3rd than second due the whaletail starting to work.
Also because it is dialled in progressively it starts weight transfer backwards before it gets to peak torque, its not like a full bore gear change with a massive turbo where you get hit with the whole lot when you change gear, I had the controller set to reset on every gearchange to dial it in smoothly again.