Which version of the Xcal?
All of them have a limited number of ECU's they can program, known as "unlocks"
I had that issue with my Xcal2. Thought it would work for my ECU (it did) but it was out of unlocks. Had to send it to SCT to have them reprogram more unlocks....didn't cost as much as a new one but just something to be mindful off.
The Xcal is very powerful. You can datalog all the ECU parameters and even external parameters (like a wideband air/fuel gauge). It will also be required if you plan to do any engine mods that will require tuning (whether it be remote tuning or dyno tuning)
2004 SVT: Boost soon!
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2007 ST ; formally bewst'd - R.I.P