Looking for some mods for the new to me suburban premier with 60k miles. Would like to do some coding for seatbelt chime and stuff like that. What’s some good and maybe free software for that?

I tow my x45 boat fairly often which is in line with the tow capacity, unfortunately not the max package. I might change the differential to a 3.42 or 3.73 at some point but what’s the best tuner mainly for firming up the shifts a little? I’ll be installing a bigger cooler soon. The trans temp stays under 185 but I haven’t checked while towing yet.