Faulty New Water Pumps?

My GT6 (Mark I with Mark III engine) overheats despite a new, high-density 
radiator core, cool thermostat, new 7 lb. rad cap, electric fan blowing in 
correct direction, etc.  It has a new pump from Vic-Brit as well, and I 
wondered if that might be the weak link.  Anyone have poor luck with a new 
water pump?  Any other suggestions?  Thanks!
George Haynes

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