Can you buy another car down the road if you have been making payments on a truck you never use and you can't afford the payments anymore if you repo the truck?

YES, you can. It may be harder to get financed (bigger DP and/or higher interest rate) but you can. You WILL have to pay the balance due on the truck so seriously consider SELLING it. You may have to put money with the selling price to get the loan cleared but it will be MUCH cheaper that way.