1987 Chevy Silverado Truck died and won't restart

I was driving down the the highway, and my truck began to slow down. If I pressed the gas, it just whined but didn't speed up. Then something popped, the truck died, and the coolant began boiling over. I pulled over and popped the hood, and the boiling coolant was the only thing I saw. Now, the truck will crank but won't turn over. It is a propane powered truck, so I don't know what effect that would have.

Thanks!