overheat

I have a 2004 800 RMK 151" vertical escape. Purchased used a few years ago. I love the machine, but I am always fighting overheating problems, in all snow conditions. Over the last two years I have added a temp gauge (to know where I am), added scratches, changed and extended the snow guard...

long story short. Bought a 05 rmk 900 today filled it up with super and ves gold. Started her up all was going super for around 1/2 mile then I coasted to a stop engine just stopped, steam coming out of the cowling, leaking antifreeze on tank. Pulled her over a couple times (seemed harder)...