I don't think the radiator will cause the tranny temps increase. Many guys on a truck website that I am apart of have tranny gauges and high stall torque converters. They use both the radiator and a secondary cooler. there tranny temps stay around 150-160 but the thermostat the same trucks is a 195. I think the radiator part mainly just stablizes the temp variation. Not too cool and not too hot.