I'd keep the Shelby and find a really nice older supercrew F150. Your Shelby is a great car - and nicer than most of them out there. An older F150 won't have all the bells and whistles, but can still be super nice. I love my brother-in-law's 2004 FX-4 supercrew with the 5.4, leather, loaded. One of those might run you $15k tops these days - as compared to $40k or so new. And it wouldn't depreciate much more if you'd take care of it, which I assume you would based on how you keep your Shelby.
If you do decide to sell your Shelby, what would you ask for it? I know a guy who might be interested.
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