Loss of power when warms up

Hello guys,

I dont know much about cars but here is my problem.

I have a 89 Ford Bronco 2 XLT

When i first start it in the morning when its cold down, The Truck runs GREAT!! But when it warms up I loose all power what so ever.

I changed the Radator cap, Fuel Filter, Hollowed out the Convertor, The Thermostat works, Flushed out the Radiator.

The Collent in the overflow where you put the antifreeze in like boiles when it looses power.

last thing i cant think of is the water pump, but if that is it, how do i check it to make sure its working or not, without taking the engine apart?'

Any help would be greatly appreceated!!

Sean