it would be tough to have them say anything about a warranty claim on the manifold. with the shroud in place, to the naked eye it doesn't look any different. without a dealership being able to PROVE that the bolt-on part was the direct cause of the product failure, they have the option not to cover the repair. but voiding your warranty with a bolt on would be next to impossible. they do repairs on a claim to claim basis. just find a GM shop that sells after market intakes and chips and know you can trust them with your truck.
These manifolds have been flying out the door like pancakes. They help throttle response and also bring down the egts by about 50deg. Fairly easy install as well. Definately worth the money. Even stock Dmax will benifit from this. Doesnt have to be high hp to see the benifit.