when a tuner/builder sends you a custom SCT file, it will be like any other typical file. It will have a name with a . and 3 digits, similar to how acrobat is ".pdf", but it will be either .LL3 file signifying the "Live Load 3" program you'd need to use to load it, or a .XTR file signifying the program "Extreme Tune" that would need to be used. The ".LL3" files and the Live Load program are the newer versions, but they all work well. I have both .xtr and .ll3 files on my computer, and generally what you get will just depend on how the tuner/builder outputs it from the tuning software.
Before loading the file onto the SCT tuner, you can sometimes set certain parameters to further customize the file for your truck like tire height (generally revs/mile), idle rpm, etc.
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