what exactly does turning the tow/haul mode on do?

have any of you guys tried racing with it on? does it help or hurt?

 

It delays the shifts to help prevent wear on the trans when towing or hauling a heavy load. I don't use mine for racing, it makes my truck shift from 1-2 at 5200. Stock is 5600 and with my HPP, I have my shifts set for +3 which is 5984. It must override the HPP because at full throttle it'll still shift at 5200 even with the HPP setting. It's nice for is what it's designed for, keeps the trans from hunting for the right gear.
Jim