GNeely,
I have one, and the increase in fuel mileage is minimal -- perhaps 0. 5 mpg. You will not even come close to paying for it in fuel savings.
That said, I consider it to be one of the best accessories I've ever installed. The ability to split gears is great, especially when towing.
The installation is difficult, with poor instructions. If you are not handy, you should consider paying someone else to install it (adding to the cost). I see you have the right truck configuration, but some 4WD drivers will have to cut a foot off the front of the plastic fuel tank in order for the unit to fit.
Don't expect any improvement in mileage, but buy it. You'll like it.
Loren