I would suggest if you get test drivers, you do not tell them whether the “improvements” are connected or not.
I’m also 77 and still do the 1500 miles to CO in 2 days… 8+ round trips in a 04 Dynasty (80K miles on it) and another 3 in our 08 Navigator. Other than adjusting the TRW boxes, the Dynasty is at 100K miles (still in the family) and the Nav at 70K miles… everything is original.
OK, instead of throwing the Safe-T-+ previous owner put on the Nav, I made it adjustable on the fly. Not sure how just adding a tag axle makes such a difference in a rig that wanders, but glad it dies as I love driving the S-10 chassis.