I have a 2004 GMC Sierra that is having problems when I try to fill up at the gas station. To begin, every time I take the gas cap off to fill it up there is a lot of pressure that is released. The problem is that when I start to fill the tank I can only get 3 gallons in and then I have to wait a couple minutes and then I can only get 1 gallon in at a time until it is full. I am suspecting some type of a venting issue but I am not exactly sure what to do. I searched the chevy and the GMC boards and could not find anyone that has had similar problems. Your help is appreciated.