I have never had a pump cause overheating except when they lost coolant. I have heard and seen photos of pumps that had rusted vains and could not pump enough coolant to keep up with the demand.
I have had a jeep six cyl with just about the same problem you are having. It was a carbed yj and the timing was not advancing enough. The retarded timing caused the overheating.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

professional bovine relocation specialist