Back in 1975, the MM warranty act was written and signed into law primarily to define all manner of warranties and to create a standardized language for all US manufacturers to follow - whether they be an auto manufacturer or a kitchen appliance manufacturer. Included, as a minor point, was language that helped to protect aftermarket auto parts manufacturers with regard to auto manufacturer warranties. Before MM, Chevy/Ford/Dodge could deny your vehicle warranty after installing just about any product, no matter whether that part had been a factor in a covered failure.
After MM, auto dealers/manufacturers were/are (theoretically) required to prove that a modification either contributed to or caused a covered failure - before denying coverage.
Warranty disputes are generally handled through arbitration, where a fair-minded third-party hears both sides (usually someone familiar with the automotive and related industry), then arrives at an equitable settlement. It's worth noting that the auto manufacturers win approximately 90% of these cases, cuz it's really hard to prove that an aftermarket part didn't "contribute" in some way to the failure. What this really means is that the vehicle owner has the burden of proof. Some of the larger aftermarket companies (i.e. Banks) have provided engineering support in arbitration cases involving their products. This is a big help in resolving a dispute in the vehicle owner's favor.
That said, GM has begun selling performance exhaust systems for their diesel pickups, and the last time I checked, they sold performance air intake kits for quite a few of their gas powered vehicles. These are (or can be) installed at the dealership, and your vehicle warranty will cover the new parts as though they came on the truck from the factory.
To take this logic a step further, you shouldn't have a vehicle warranty problem following the installation of an aftermarket product that doesn't alter boost pressure or fueling. Products that passively make the engine more efficient, like exhaust or intake systems, shouldn't affect your warranty (except for oil contamination of the MAF sensor).
Now, everyone should know that any active power modification can put your warranty at risk. Active power mods would include performance products like chips, modules, programmers or tuning. How strictly this might be enforced depends on your local dealer's interpretation of GM's official warranty policy. Some dealers are lenient and some are "letter of the law" types. We here at The Diesel Page suggest you discover which type your dealer is by talking to your dealer service manager before installing any active mod.
Check with www.sema.org for more information concerning MM and to learn more about your rights when installing aftermarket parts.
Jim