I know the radiator is new, but is the condensor perfectly clean so as to enable good airflow to the radiator? I would replace the water pump, as they are cheap ans is a ikely cause of your excess heat. Also, is it the same tank of fuel for all these tests, as higher cetane could possibly have an affect under high load. The stuck brake/ bad master cylinder sounds most obvious to me. Try putting it in neutral and pushing it, or better yet, rais it in the air and try to turn the wheels.
I had a leaky master cylinder that caused brake drag and the fluid leaked into the brake booster - I sucked out about 20 ounces of brake fluid from the power brake booster!! I gues the PO had just kept filling it up when low.
Good Luck, Adam Bush