2006 Hummer H2

Hi, I have 2006 hummer h2 with only 25000 miles and its idling rough and not running smooth as it used to be. Its still under warranty. Went to the dealer couple of times but he said there is no any code everything is normal. When I push the accelerator pickup is not that good. Sometimes when I push the accelator rpm goes too high before it switches to the next gear because of pickup is not good and when I turn off the key there is hissing noise coming out of the steering wheel. Dealer told me that there is a bearing inside it and that hissing noise is of that bearing when ignition key is turned off. Can anybody help please to findout what is the problem with it. Its doing that for more than a year. Could it be something wrong inside the engine, maybe sticky valve that is causing low power output and rough idling. Please help. Thanks a lot.