I completely rebuilt a 66 200 from the ground up. Now it runs great but will only generate 30 psi pressure on start up and it drops after it has run awhile. I have replaced the new oil pump with the one I took out from the rebuild which was fine before but they both did the same thing. I have gone to heavier wt oil and changed the filter but still no dice. I checked the pressure with 2 external guages and they both verified the same thing. But I have no leaks anywhere. I am at my wits end. Any other suggestions you could have would be greatly appreciated.