I have a Hypertech Max Energy for my Cummins and I have been very happy with it.
You will not see any significant increase in mpg no matter what the tuner maker claims. It just doesn't happen.
You will be risking you warranty, and you need to consider that in your decision.
You will get added power that is fun to have and in my experience using three different power adders on two different trucks, there is no penalty in mpg for having that extra power until you get up into the higher levels of added power that are not safe for towing.
If you have a DPF equipped Duramax (LMM), I would leave it stock. Tuners and DPFs do not get along generally. You may even lose mpg using a tuner with a DPF equipped truck as the higher power produces slightly more soot in the exhaust which uses more fuel more often to regen the DPF which = lower mpg.
2010 Cougar 322QBS 5er
2007 Dodge 3500 SRW Megacab, 4x4, 5.9L Cummins, 3.73, 48RE auto HYPERTECH MAX ENERGY or DIABLO PREDATOR tuning MBRP 4" Turbo back Scangauge2 for Boost, Coolant temp, Rail press & Trans Temp
Torklift Stable Loads