OK, I replaced the OEM radiator with a triple row, welded aluminum radiator. Replaced the cap. Fans are working. Now it runs cool if I don't throttle it much, but with half throttle the car overheats. Hills, acceleration, passing cars are just to be avoided! I keep filling the overflow and purging the system. Do I need a new water pump? It's not leaking.
You can find tips on diagnosing an overheating condition in the FAQ.
Did you replace the thermostat? Is your lower radiator hose soft and collapsing under pump suction? How old is the water pump? If very old it's possible the impeller is loose or corroded. If all else fails you might want to check for a head gasket leak.
I've had the van pretty much since new and have never seen any rust colored antifreeze solution. I don't think there's any corrosion in there.
That thing is over 2 decades old and overheating, everything has to be considered suspect.