Modifying the stock ECM is one thing, but replacing it entirely really does open the door for the MOCO to mess with the owner when warranty work has to be done, or if you break down on the road somewhere away from home and they can't hook up to diagnose whatever problem. It just gives them a really good excuse. Of course, saying something totally unrelated to the ECM is not warrantied because you've changed to a third party vendor is absurd, but they'll use whatever excuse they can at times, and some dealers are known for their absurdity. I had to get a new FOB paired up a few months ago...just to be sure there were no issues, I downloaded the original program into the ECM rather than the one modified by the TTS Mastertune before I took it in. I'd just rather not argue with them about BS.