My 5er weighs in right at 10K fully loaded, and my 08 Duramax weighs in about the same as yours. I too wanted a little extra for our trip west in September, so I purchased the BD Diesel VVT Turbo brake. Banks has a very similar product called the "Speed Brake". While MI does not have moutain grades, I did have the opportunity to test the unit on a fairly long (3/4 mi) 5-6% grade after the installation and I was impressed to say the least. The VVT brake does require some rpms to achieve max back pressure, from 2300-2800 rpms worked best, providing substantial retarding power. I`m happy so far. I would recommend checking it out.
