Thanks for the insight. Maybe I'll just leave it alone for now and go by what my GPS shows for speed. I still don't like my GPS for miles driven because that's not spot on either. So for miles driven, just for my own worthless peace of mind, I'll just manually convert what my odometer says by the factor I know it to be off.
You had mentioned; "...theres not much mechanical left in these trucks." That said, it's even more surprising to me in this day of computer age that these sorts of electronics aren't only easily infinitely adjustable, but also easily done by the vehicle owner. I know, I know, it's about money. What would the dealerships do if they couldn't charge customers $100.00 just to hook any given vehicle up to they're coveted electronic diagnostic equipment. Such is life. Maybe soon there will be an app for that (not a free one of course).
If anyone else has anything to add, please do so. Thanks, and Happy New Year Everyone!!!