Are all the hood and radiator seals in place? Did you replace the radiator hoses? Did you replace the radiator cap? Do you have the correct sending unit? Have you used an infrared thermometer to verify running temp? Have you checked the coolant level? Are you losing coolant? Is the thermostat installed right side up?
165 degree thermostat is on the cold side and probably won't close allowing coolant to cool in the radiator. Have you done a compression check? Do you have white smoke coming out of the tail pipe?