I have a 5.3 with 276k. It went through two transmissions, exhaust manifolds, brakes and brake lines, starters.
need ball joints, lucky to get 15mpg.
I have a 5.4 with 154k. Muffler and tailpipe, brakes all around due to rust, Fuel filler neck, It needs a exhaust manifold or two. This truck is 2 years newer but the rust is horrible. Just bought a sandblaster to try to clean it up. I get about 13mpg with this one.