Your point isn't proven at all. Actually its quite the contrary. Diesels sell for 10-12k more than gas. And you just proved that gas engines a few years later are selling for about 10k less than a diesel. You are trying to show that you make up "so much" at resale, but in reality, you paid less for the Hemi, payed less to run it if you arent towing daily, and your truck is now worth the same as compared to a used diesel that cost more monthly as well as cost more to run, if you arent towing daily.
I notice you never really addressed your truck being listed for 35k, you only addressed it still being there
So the dealer is willing to take a 8k loss to give you a good deal? Or they really actually gave you 32 and you added 10k to make it look better for this argument?
If dealers lost 8k on every deal, they probably wouldnt stay in business. Just because they gave you 42k and had INSTANTLY listed it for 7k less, doesn't mean that happens every day. If your story is true, which its not, its a one in a million story and should not be used for resale value arguments.