I just learned that the OEM water pumps should pump 9 gallons per minute. My original pump came nowhere close to that, maybe a couple gallons a minute. Tried tons of stuff, and eventually replaced the whole water pump. Worked for me.

Your new problems do sound to me (amateur) like a carb issue, but could need adjustment, a good cleaning, or a rebuild (new seals, etc). There is a quick check you can do on the "power valve" on holleys website if you google it. Have you ever had the engine compression tested? Good luck