Your experience is one of the reasons it's really important to avoid car payments (at all if possible!) on old vehicles. There's nothing worse than making a note on something that's leaving you on the side of the road or eating you alive in repairs. You're in a worse situation because diesels can be outrageously expensive to repair. We have several in our fleet at work and I'm always disturbed by how expensive they are to fix.
If you can sell the truck and break even, you might be better off going that route; a diesel Ford will still be worth something; a 2003 Dodge Durango is just about fully depreciated. From a financial standpoint it's almost always more sensible to drive the fully depreciated vehicle and sell the vehicle that still costs money.
Example: 2005 F250, worth $15k, owe $15k, $300/mo payment; 2003 Dodge Durango, owe $0, worth $4000, no payment
If you sell the truck and break even, over 1 year you will save $3600 in cash (let's assume no repairs for simplicity). The Durango might be worth $3000, so you've got $6600 in equity. If you drive the truck and sell the Durango, you'll get $4000 for the Durango, spend $3600 on the truck, and maybe "earn" $1500 in equity on the truck. That gives you $1900 in equity, but you've still got an old truck. If you do this for 2 years, you save $7200 in cash, the Durango is worth, say, $2000, so you've got $9200 in equity. If you drive the truck, you spend $7200, you get $4000 for the Durango, and you maybe have $4000 equity in the truck. That leaves you with $800 in equity. See how you keep going backwards? There's no way to overcome the vehicle payment until it's gone.
So what you really have to gauge, from a financial point of view, is how long you can do without the truck until you save enough money to not have a payment at all.
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