99 Silverado Overheating

[mcbassin]

I know this is the LSx swap section but I figured it would be the best place to ask.
My daughter drive s 99 Silverado, 5.3 engine. Yesterday she calls me and tells me a hose popped and it was spraying stuff (coolant).
She sent me a pic, I told her it was the heater hose. I told her, see if you can lock it back on and get some premixed coolant. Long story short, my son filled the coolant back up through the top radiator hose once the truck cooled down.
By the time I get off work, they call me and said it went about 1/2 mile and got hot again.
I drive there, and fill it up again through the top radiator hose. It appears to be completely full of coolant. I gave her my car and drove her truck home (about 7 miles). I had to stop to let it cool down a few times.
It's really weird to me, almost like the water pump is not circulating the coolant.
I changed the thermostat last night, just because it's a quick fix. But it didn't fix it. I let the truck idle up to temp, it seemed fine but as soon as I drove it about 1/2 mile the temp shoots up again. I had to let it cool down then return home.
The truck is a high miler (235k+) and all stock, the thermostat had been changed before. i.e. the goop job for make a gasket they used. The motor has tons of power and runs great. Doesn't consume oil or anything. There is no sign of head gasket or cracked head, no steam from the exhaust and the oil is clean.
I'm not into just throwing money at experimentation.
Has anyone experienced a water pump impeller failure or similar?
The coolant looked really clean and it doesn't appear the engine could be stopped up.
Suggestions?