I have an 06 3500 4x4 SRW, and I went with the Smarty also. I have had the full Banks powerpack before, but it's touchy with dealer warranty issues, whereas, the smarty can be "removed" when you take it to the dealer, and they don't know that you have "violated" any of their rules. My truck has had the smarty on it, since about 50k miles, and I run # 1 or #3, most of the time. #3 is the most fun to drive, has a nice smooth spread of power. I even had the transmission "rebuilt" under warranty at my local dealer @ 97000 miles because it was slipping under heavy load. They 'checked' my codes and computer, and all that they could tell me was that I have a heavy foot (5% full throttle use).
I tow the max CGVW, and I cannot recommend using the smarty while towing for long runs. The black smoke (even on #1) that the smarty puts out over the course of 6-8 hrs+, gets black soot all over my 5th wheel. I do not have guages yet, on this truck, and that is why I don't use any setting greater than 3, since I can't monitor anything (will get something soon). I have tried many various settings to elimnate the soot issue even on #1, and have contacted Marco directly, but haven't been satisfied enough to tow long runs on #1 (nice improvement in power though).
On setting #1 I have noticed up to 1. 5 MPG improvement over stock, consistantly. On # 3, I only get about . 75 better, and sometimes worse, because my foot gets real heavy, since its soo much fun to roll that power on. My MPG ratings are documented each tank, and my driving habbits don't change, but I do know for sure that if I slowed down to the actual speed limit, I pick up almost an additional 1mpg, just driving it "like an old man".
Long story short. . when in warranty, stick with the Smarty-(be conservative). Outside of warranty... take your pick, and "become your own warranty station".
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