Depending on the price of the new truck and diesel it will not be worth it. I work for Dodge I've seen tons of people trade in for a diesel just for fuel mileage. If you need a diesel then go for it. Let me know if you need any parts.
Oh and what Ram gets 25mpg. The 5.9L 2wd were lucky to be getting around 20 21. The 6.7L pssst. Keep in mind too if your buying new that our diesels take around 60-100k to break in to be getting better gas mileage too.