I was interested in this and did a bunch of research. What I found was that this is a common problem when there is too much tongue weight and the roads are rough (with some cases involving northern salted roads and rust).
I found pics of Toyota's, Nissan's, Fords, Dodges and even an old Chevy all with the same issue as well as a whole thread on problems with Chevy frames from the early 2000's to at least 2013.
In the end it appeared to be too much tongue weight / trailer weight and too rough of roads.
it appears that you could get away with all sorts of things on good roads but hit the potholes hard enough and life changes when you are way overloaded.
