if you do a delete you will need custom programing to drive the truck, stage 1 deletes the EGR and does some other mods to timing and fuel delivery, stage 2 delete requires removal of DPF and def systems to function and has more changes to the programing.
I have stage 1 on mine and it is a SFT tune, I have heard that recently some people have complained about some recent changes the company has made, don't know about the changes, but my tune is good. Its a totally different truck with it, and this is the second truck I have used SFT for. NO THROTTLE LAG!! way faster gain in speed, mileage stays about the same for me cause its just so much fun to get on it all the time. My tuner has a trans tune that alters shift points as well..lotsa fun.
I plan on doing stage two in the near future to see if the changes are as good as they say, but don't have first hand knowledge of it at this time.