mild/2 only gave me .5 mpg better than my stock truck if my truck didn't go into a regen on a long road trip. Including all the regens from my stock truck the mild/2 tune probably nets about 1.5 mpg gain over a stock truck. mild/2 isn't the tune for best mpg's, but its a safe smooth tune that feels very natural for our Cummins 6.7.
In regards to mpg's:
mild/3 is slightly better than mild/2
wild/2 is slightly better than mild/3
wild/3 is slightly better than wild/2
wild/4 is the best hands down for mpg's.
I never even thought about wild/2 being an option, but everytime I tow with my timing on level 3 the mpg's drop when compared to level 2 timing. I always get better mpg's towing on level 2 timing, so I figured why not leave the timing on level 2, but inject a little more fuel with the wild tune and so far its a great tune. I'll report back further details when I get to tow with it. A lot of this has to do with how you use your truck and what axle ratio you have and tire size. When you look at the timing charts from H&S you will find that based on rpm's alone it will place you into a slightly different timing degree before top dead center. You have to find out exactly what speed you wish to drive or tow and then find that rpm and then match your tune for your exact truck specs.