Bring up the fact of the magnusson act. This act allows aftermarket companies to exist without dealerships dening warrenty work. Case in such, you use amsoil synthetic motor oil that may not be API certified and a crankshaft bearing goes south. The dealership and manufacture cannot deny work because of the oil. Same goes for a liftkit, bigger tires, exhaust, or intake. You will have to push the issue but you will win. I have been there done that. Infact they cannot deny work for a programmer either. The only way they can deny work is if they can without a doubt prove that that aftermarket part caused said part to fail.
dieselman77