Three observations:
I had a silverado z71. From 2003-2006 (mine was 2003) The frame rusted out to the point I couldn't get it inspected or repaired. It had 84,000 miles on it. I also had a tahoe, three years older, double the mileage, driven on the same roads and kept in the same garage. Nowhere near the same issues.
My brother in law has a 2007 tundra. Negligible rust and 275,000 miles on it. Not many repairs to date. I went to buy one in 2015.... kinda ugly inside and out. Bad reason not to get one... but it was important.
I bought a 2015 F-150 V8. Best vehicle I've ever owned. It's like driving my living room. No repairs, same brakes, same tires. 69,000 miles. Will have it inspected in Nov. and brakes and tires will go one more year. Maybe 80,000?
I've been having Krown undercoating. No rust on the frame. The body is aluminum. I live in snow country. Maine.
First non-GM vehicle I've had in 48 yrs. Maybe should have abandoned them earlier.
All in all.... it's sort of a crap shoot each time you get one. Good years, bad years.