There's a good chance you will have to buy new tunes if you changed the ECM. Like Brad said, the tuner is licensed to the ECM serial number which is unique to each ECM and cannot be changed. Then there is the fact that most tuners send out the AutoCal with 1 available VIN license slot, and only the tuner who is married to the AutoCal can change that. The AutoCal can be unlocked to add another VIN license slot, but once that is done, the tunes currently on there from Rob will no longer be available. There is also the small possibility that the file itself is also locked to the ECM serial number which means that even if you do have an open VIN license slot, you still may not be able to flash it. You can download the EFILive V8 software and check some of this information out to see what you can or can't do. I will also add that I have not seen many LMM ECM failures, and I would do some thorough diagnostics before replacing the stock ECM.