At what point does it make sense to buy a newer vehicle rather than put money into the old one, and have I reached that point?

To be up front, I realize how many times this question has been asked, and I know the correct answer is "depends on what you want to do." That said, I'm still looking for validation for my decision in hopes that it will (somehow) lessen the hole in my wallet.

I recently brought my truck into a mechanic for a couple issues, and he gave me a rough estimate of $1,100-$1,300 to fix the issues. It's quite a bit more than I expected, but it's nothing too bad. However, it left me wondering at what point I should start looking into a new vehicle.

The truck is a 2005 Chevy Silverado with around 250k miles (about 1/4 of which are mine), and it's my first truck. Got it when I was 15 for $4,000, and in the past 5 years, I've spent around $1,500 in maintenance - not including the cost of this latest repair. The frame is solid, and after this fix, it should be good to go for a long while.

I want to keep driving it 'till the wheels come off... or until the cost outweighs that of a new truck. I don't think it's reached that point yet given the cost and hassle of a newer vehicle itself in addition to the insurance, tags, etc. Even if I continue to spend 1k every couple of years, I think it'd be more affordable given my circumstances (in college and already 12k in debt). What do y'all think?