Pressure in my cooling system

[cfilm1]

In the city my 74 Bronco with a 93 5.0 motor and crossflow radiator runs cool. As soon as I get on the highway the systems burps out of my Be Cool catch can and thus progressively as the water escapes the system the motor begins to run hotter. The mechanic that works on my cars says the block might be warped. We just had the heads resurfaced and new head gaskets installed and he thinks compression is entering water jackets there. I see no water in the exhaust though. My brother wants me to change the water pump thinking it might be cavitation causing pressure to build up. Any ideas or knowledge on the subject would be greatly appreciated. This is the third time this month I've had to ride home in a tow truck and AAA is about to drop me. I stink like antifreeze please help.