Don't forget it depends where your dad is in the progression of Alzheimers, Nikki. If the specialist thinks he isn't fit to hold a driving license, then that's one thing, and if he's forgetting the names of his children, that's another. In general, people don't usually begin to lose names of close family until they are some way along.
For example, my dad is perfectly fine taking most decisions for himself and needs no help at all, but like many people his memory loss is patchy and some days he is better than others (he has vascular dementia, so the decline is slow).
Dad can remember the name of our daughter, who he seldom sees because of geography, but he can't remember he has a dental appointment, or even a story he told two minutes ago. He still thrives on being asked advice because he likes to help, so we ask him questions even if we know the answers because it helps with his mood and self-respect and how he sees his position in the family. There are practical things you can do for him like get some fridge magnets that show the date clearly and putting up lists of phone numbers, but it sounds like your mom will have a handle on that.
If you can play into your dad's strengths and preserved function, there's a lot you can do to ease his frustration, but also much more you can do to help your mom, who has to live with him 24/7. She's the one who will take most of the stress.
Chrissy has a good point about keeping the insurance on in case of theft, but it sounds as if you are thinking of selling the truck, so it needn't be arranged for long.
