Old truck vs new truck

It likely comes down to disposable income. Your 05 has the potential for many more miles in it. That doesn't mean it wont need some attention here and there, but the likelihood of a major repair is not zero but not very likely. If you would rather upgrade now, rather than later, your truck will have excellent resale assuming its in good shape, miles are certainly right. I would think that should be worth 25K and if so your 1/3 the way to a fully equipped '19 3500 diesel and even better on full option gas version. Just comes down to what it is worth to you. Like the saying goes your trading your time for money and how much of your time (life) is worth paying for a new truck. Me its worth what it costs, but everyone is on different path.