T-250 rear brakes

Every 20,000 miles I have to install new rear brake pads. At 40,000 new pads and rotor. At 60,000 they are worn out again and the original front pads are still good. This is opposit of the normal front pads wearing out first. What gives? The Ford dealer has no answer

My guess is bad proportion valve. It is normally supposed to give something like (can't remember for sure this amount) 70% to front then 30% to rear. Sounds like it is giving too much to rear which are designed to not get as much usage. Too much pressure equals overusage and greater wear.