Recently I've had to use my 2008 Sierra 1500 WT for some 2 hr runs. I found that I didn't need to keep the AC on all of the time but instead got the truck cold and turned the AC off and pressed the inside circulate button. With low fan speed it kept the truck cold for most of the trip. Less load on the 5.3 V8 which helps the gas mileage . Seems to work . FYI
