What is the purpose of a factory stabilizer package (rear stabilizer bars)? The truck is a 2007 F250 SuperCab.

 

It's actually the Camper Package. These trucks are built with the idea that they may be used to haul a slide-in camper which greatly raises the center of gravity of the truck. The rear stabilizer bar acts to resist body lean in the corners which adds stability to a top-heavy truck. Every vehicle I've ever heard of has one in the front, but most trucks don't have them in the back except for those equipped like yours.