i have a 1994 Gmc 1500 with a V6. the truck has been over heating so i changed out the thermostat and it still was over heating. So i toke the old one and cut the top off of it so it was free flowing. and it still is over heating. But then i got really looking at ever thing and the top and the bottom radiator hoses look like they are going to pop with the truck is running. blocked in the motor maybe?

 

let it cool off and run it with the radiator cap off and report back, me thinks it could be a head gasket, if there are lots of bubbles its almost a safe bet