Turn the traction control completely off, put it in manual mode 2nd and start roasting them, don't push the throttle right to the floor though, then when they are good and warm you should be able to shift up, again only like 3/4 throttle and don't use diff lock or traction control kicks in
I am on my second mishimoto and it just started leaking as well. At least they are lifetime warranty just the pain of changing and replacing rad fluid. I wish there were a better answer. But I believe it is the flex in the frame.