My 06 Buick Rendezvous keeps overheating, within minutes of driving.

Hello, sounds to me like you have an air pocket still in the cooling system after replacing all these components - causing the coolant to boil over. I can't be sure what was done to purge air, so - check this first? There are no mysterious cooling system components here. You require coolant flow, air flow through the radiator, and a thermostat that opens and closes at the right times. You also need to have an engine that is intact when it comes to isolating coolant from the combustion chambers. I'd suggest a professional assessment at a shop near you. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops