I have only cooked bison twice, but I treated it as I would grass fed beef. Due to the lack of fat, it needs not to be abused over extreme heat. If they are steaks, cook over gentle heat to no greater than a medium rare. If a roast, cook slowly to no more than a medium rare. Using to great a heat shocks the meat . . think of kneading bread and then immediately trying to form it. You can't because the proteins are tight. . . the structure has not have time to relax. It is the same with very lean beef, bison, venison, etc. Extreme heat shocks the meat and it toughens.

Carefully!!!

What sort of cut do you have or are you thinking of? That will determine how you cook it. The important thing with bison is not to overcook it.