The roof is the real killer there. The rest of it could be expected from a high mileage vehicle/luck of the draw and, as has been mentioned in previous replies, maintenance is a factor. Typically you are either putting money into an older vehicle for repair/maintenance or you're making payments on a newer vehicle and not worrying about repairs so much. As I do as much of the repair/maintenance work on my vehicles as I can mechanics rates only sometimes figure into the equation of owning an older vehicle for me. Mine is in pretty good shape for a northeast vehicle...though I've noticed my first body rust at the top of the rear wheel wells last week...so at 164k I'll be holding onto it for a while. If your truck hasn't been seriously abused and/or neglected for most of it's life then I'd think it has more life to it, especially if you do any of your own work.

Good luck, Mike