The 2.9 Ford was much more prone to head gasket problems than the 4.0. The 4.0 had a bigger problem with cracked heads. It was such an issue that in the late 1990s Ford created a new head casting to help with the problem, and retrofitted these newer castings on vehicles that came in needing warranty work for head cracks. The Mazda I owned had already had these newer heads installed, which solved most of the problem.
I knew why the head gasket blew on that truck...I exceeded the truck's design parameters.
It sounds to me like what has really got you down is the fact that your new car is now a well-used car by any reasonable definition of the term. And I can understand that.