In the summer of 2004, Toyota began extensive offroad evaluations of the FJ platform by driving development mules on many of the most difficult trails in North America, including Moab, Utah, the Angeles National Forest, the Mojave Desert, and the Rubicon Trail. Despite each one-off mule costing hundreds of thousands of dollars, the development team was determined to push the capabilities of the prototypes in order to deliver reliable offroad performance in the production model. Changes to the A-TRAC traction control system and suspension tuning came as a direct result of the prototype testing.