Well, it's a gamble just like any equity or "investment" these days. They could go up, they could go down. But if you sell you know for sure you will NOT have it, and it MIGHT be harder and more expensive to replace with an unknown truck, using depreciating dollars, and you still then again have to pay new taxes on it so the money you "make back" will be eaten up again and you'll have paid the same tax, twice.
A year ago, I was casually looking at used cars and trucks and buying buying buying anything that interested me that seemed like a good deal. I let some slip thru my fingers but overall did well. All of my vehicles have increased remarkably in value today, but I'm not selling any of them.
I'll note, a year ago a nice low miles 10-15 year old Mustang V8 could be had for about $10,000. Yesterday I called on one that was admittedly a bit more rare and low miles and nicer than an average Mustang. I was expecting about $20k. The dealer told me it was $40k. I nearly chocked on my coffee... Um, no. $40k, for a 14 year old Mustang, even if a bit special, is not going to happen.