I hate to give up on a good vehicle then it has served well but it might be good to look at what is available on the used truck market.

The value for money is almost always on the used side because you pay a huge premium for new. That first mile driving away from the dealership is the most expensive mile you ever drive. Modern vehicles are increasingly reliable as they push past a quarter million miles. Back in the early 60s getting 100,000 miles was something of a trick and required gentle driving and meticulous maintenance. Now you might get 100,000 if you do nothing but add gas. Assuming they bothered to perform the bare minimum of maintenance, and you keep it up, and don't use it in a demolition derby, you can pretty much expect to get 200,000 miles from any mainline designs.

Bottom line is that there is often a large supply of used trucks out there with less than 75,000 miles that are in good condition. If possible avoid dealerships. Ask around and scan the papers and local trader pages. Paying with cash and buying from the owner can save a lot of money. I'm down south where trucks are really popular but I've seen good ones where they are only asking for $4000. Given the cost of body work, $4000 won't go far, a different truck may be the way to go.

I'm not saying you shouldn't repair Old Reliable. But given the sort of prognosis a vehicle has once it has rust working from the inside out, rust working in the nooks and crannies you can't get to to treat, and that a new/used truck may be better than what you have now, there are clearly limits to how much you can spend on repairs before you're behind the curve.

Such situations are always a PITA .