[shall36]

The original question kind of got things down a rabbit hole. The OEM radiator IS aluminum with nylon endtanks. Aftermarket units, made from aluminum, will likely have aluminum endtanks. Any improvement in cooling over an OEM radiator in perfect condition would be due to design differences, like the number of rows in the core or cross-flow vs. vertical flow or surface area, etc.

Using a scan gauge, my truck with stock cooling setup stays below 200* at all times. I'm in Florida with ambient temps upwards of 95* and humidity in excess of 70%.

Poor cooling is likely a result of: 1) obstruction of the radiator due to debris, 2) poor flow through radiator due to scaling or gumming, 3) stuck or partially obstructed thermostat, 4) defective water pump (impeller spinning or excessive pitting on the impeller or water pump housing), 5) possibly a bad fan clutch (would only show during stop-and-go conditions). All of this assumes that there's enough coolant in the system and there is no trapped air.