Selling my truck to save money in the long run?

I have a 2006 Dodge Ram 2500 diesel with 190000 miles. Paid for. Recently my wife gave birth and quit her job a few months previously.

Prior to this we took in roughly 8 to 9 grand a month as she was part time hourly. Now this is closer to 5600 a month after taxes. I make more but contribute 20 percent pre tax to my government tsp.

We closed on a house last month with a sizable down payment. Every month for the last 5 months we’ve been hemorrhaging money. This is a combination of the down payment, non covered medical expenses for my son, and what I feel is our excessive food budget. Also I had to do 6500 in repairs two months ago on the truck. This is approximately half the resale value. Recently a ball joint started to go out and my heater quit. I believe the engine is running fine and will last.

I’m trying to minimize expenses right now until my wife returns to work and we can start rebuilding our emergency fund back to about 9 - 12 months of my income.

Are there common cost accounting techniques to decide when it is worth it to sell a vehicle? I’m thinking of getting a minivan to fit the growing family. I would probably try to get a 2014 - 2015 with 60000 to 80000 miles. Is this stupid? BTW we have zero debt except for our mortgage.