I installed a Hellwig bar on two other trucks and they worked fine and improved over stock. In regards to warranty, just because you modify your vehicle, the change will not affect the warranty. The Magnuson-Moss
act effectively states that making modifications to your vehicle does not affect the warranty. Generally speaking, the dealer must reasonably prove your modification(s) affected a warrantied component to fail in order to deny a warranty claim. Even then, they can't void your whole factory warranty.
I worked for a ECM chip company and anytime a dealer gave one of our customers grief or threatened to void their warranty, we told the customer to mention the M-M act and the noise stopped.