try to pin point exactly where it's coming from ,sadly it sounds like a head gasket, but i could be wrong.some more infomation could help out a bit more, is the motor burning a lot of white smoke?pull the wire out of the coil and and have a buddy turn the moter over, and listen for air hissing the only true way to find out what went wrong is to pull the cylinder head off and find out. just hope it's is a head gasket blow out or a heater hose rupture, because cylinder heads are expensive, also those cylinder heads that your truck have are thin wall castings, which means they crack easily if they get too hot.hope this helps, good luck