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Figure out if it has a chip or if someone left a program in it, pull the computer and see if there is a chip installed in it, if not then it may have a program left in it or had the PCM custom burned. Either way, if you get a new programmer it probably will not work because of the previous one. IF you have a chip you can remove it and get a better one IF its not a good one.
Make sure your egt probe is before the turbo and not after it. What kinda max boost numbers and max egt numbers you seeing?
Maintenance wise, IF it were me I’d put a DIY intake on it and change the tranny fluid and transfer case fluid and front and rear diff fluid and antifreeze and add the anticavitation additive to the coolant and inspect the brakes, and steering system, and etc,etc. I like the Amsoil for the diffs and stuff, clean them out good and put Amsoil in it once and be done with it for about 200,000 miles or more.