Keep your car. Set aside an emergency fund to handle potential repairs with some of that 5k, and send the rest to the car note. Keep paying more than the payment until it is gone. The negative equity is a result of a past bad decision, eliminate it ASAP and don't allow it to continue.

Do not skimp on the maintenance of the car. Take care of it.

Rolling your negative equity into another car is guaranteed to make your debt problem worse in order to avoid a situation that may happen. A car transmission problem may never occur, and is even less likely if you maintain as appropriate.