did you find out what ratio you have now? It also depends on what you are going to do with the truck. If you have 4.11 gears and drop to 3.55 it will lose a lot of it's low end pulling power but you will pick up the top speed you want and maybe a few mpg's. If you don't tow heavy regularly this won't be much of a problem, but if you make a living pulling a trailer you probably won't like it. Another option might be 3.73 gears. They are a pretty good all around ratio. Some of the new 1-tons have 3.42 gears and are gutless. I've got a friend who ordered a '13 new and took it back 3 times because it wouldn't pull. The dealership told him to just pull in 5th. He went next door and swapped it for a '13 duramax.

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3.42's would be the next step up.