Over heating delemna??

[dillfarmer]

Yesterday on a return trip to Anchorage, I noticed a burning melting smell which quickly subsided but was followed by the unmistakable smell of antifreeze.
A quick check of my gages (running near dark at 11:00pm), I saw my alternator wasn't charging and my temp was rising quickly. I pulled the truck over as fast as I could and shut it down. A quick inspection revealed a broken belt and a bit of lost antifreeze through the valve in the radiator cap.
The nexty morning I secured a new belt and installed it... A quick trip down the road revealed rising temps (up to 220). I pilled i nto a parkinglot and (upon cooling) removed the thermostat...

Note: This is my 1968 chevy 3/4 ton pickup...

Another quick run lead to more high temps...
I purchased and installed a new water pump..
Upon an inspection of the old pump (out of curiosity), I found it to be in good condition internally....
This leads me to conclude that the problem may still exist??
Tomorrow I will install a new thermostat, and antifreeze...

Question: could the valve on the cap be causing the problem?
What else could there be??

Note 2: I'm currently stick 70 miles from home, with 3 dogs, limited funds... I really need a fix..
Any help is much appreciated...

regards...