IF your dmax is 07 or newer(dpf equipped) you need a good tuner(as mentioned) to turn off the dpf, most tuners that do this are "race only". Edge products has actually quit making their racing tuners just because the fact they can disable the emissions crap, and edge was most likely gonna have big problems because of it.
Removing the dpf system will help your truck breathe alot better and maybe gain you a few mpg's. It is technically illegal to remove any emissions equipment from a vehicle so you better check your local laws on state inspections first. If you have an 01-06 Duramax there is no need to worry about emissions crap.
Just buying an extra ecm is not going to do the trick, if the truck has 50,000 miles on it then it should have XX amount of dpf regens. The dealer see's this when they hook it up to the v2 system in the shop, and thats only one of numerous ways they can tell its been tuned.
If your worried about warranty then talk to your dealer BEFORE you do anything or you can kiss that warranty good bye, some dealers are great tho. The place i go to actually installed my exhaust and tuner for me and didnt ruin my warranty, but that was a few years ago and probably before gm figured it all out.
If you guys want a good tuner for your chevy/gm (and now cummins) trucks you should check out EFI live. I had a PPE tuner before and thought it was the best thing ever....not even in the same ballpark as EFI.
Everyone with a diesel should do themselves a favor and get rid of "dirty tuning", rolling coal is cool but too many f*a*g*s blow smoke in town and make us look stupid. Well doing so is putting diesel performance in the spotlight in the wrong way. The regulations are tightening up constantly and just like all those riding spots we used to have, its gonna get shut down if it keeps getting abused. Smoke out of a diesel is power you can see NOT USE. Unless you are running big mods(twins, tranny, dual fuelers, etc) pouring smoke is not necessary to make good power.
Just my .02
