It is Un-American because muh rights. I have the right to buy whatever I want under whatever terms I agree to, not those of the seller. And if anyone denies me that right, well hell-fire will rain down and Krackens will be released./s
Yes it is legal. It is legal because it is a contract that the two parties agree to.
Let's follow your logic:
1. It is MY truck therefore I can sell it when I want to and ask however much I want.
If you agree with that statement, then....
2. Currently it is Tesla's truck and therefore it can sell it if it wants to under its terms. If Tesla doesn't want you to resell the truck, then Tesla can put restrictions on the sale and give you the CHOICE of buying the truck or not.
There is no "right" to buy anything in the US; the buyer and seller come to an agreement (contract) to exchange goods for compensation. If no agreement can be reached, the sale doesn't happen.
You cannot force Tesla to sell to you on your terms any more than someone else can force you to sell to them, on their terms. If I demand you sell your truck to me for $100 after a year, you can/should turn me down. I can't force you to sell it to me at my terms, we have to reach an agreement.
I can force you to sell me the truck under threat of death or dismemberment but that isn't legal. Tesla isn't threatening your life or limb, forcing you to follow through with the reservation now that you have decided that you are not purchasing the truck for personal use (apparently something you agreed to when you made the reservation.) That would be illegal. If you don't agree to the terms, you walk away from the sale with your life, limbs, and buy something else.
It seems that you don't like the terms of the agreement Tesla has offered. Therefore, you have choices:
1. follow the terms (and get your truck and figure out another way of profiting from it)
2. wait until production exceeds demand and you can buy the truck without this term you dislike so much