I'm sure it's been said by now, but where you live makes a HUGE difference in how long your truck lasts... In MI, where I'm from, a truck will rust to the point of being more trouble than it's worth in 10-15 years.
I bought my current truck ('06 GMC Duramax) from ND when it was 3 years old with 120k miles, with no rust. I shortly moved to CO, and then NM. If I still lived in MI, I'm sure it would be a rusty pile of junk with no rockers or wheel wells, but I'm at 240k miles now, and planning to keep it basically forever.
Electrical stuff doesn't last in MI either... connectors leak and lead to corroded wires and modules going out, etc. And brake and fuel lines rot right off the truck. In the dry SW, nothing rusts, and nothing rots. The paint gets baked off, but it still doesn't rust much, if at all.
Suspension parts can be replaced, engines rebuilt, seats recovered. Truck frames seem to be built pretty solidly these days, so frame cracks are not as common on high mileage trucks as they were in the past either, in my experience.
The irony of it is that my truck is 10 years old, and I've had it for 6 years, and the value really hasn't dropped much, thanks to inflation and new trucks costing so much... And I have not desire to replace it with something newer... Planning to be buried in this truck. Unless we move back to MI...
C