I would take the hit on the Mustang and get out from under the payments, once you are upside down on a car you will always be upside down. Pay cash for a replacement, if you roll what you owe into the new car you will be even deeper in the hole and paying interest on a car you don't have anymore. But don't go by me, I'm weird that way. I am making payments on a pickup that I don't need and spending my allowance on a Miata I paid cash for.