The 2017 model improved to five stars in all categories, although it must be clearly stated that the only vehicle mentioned in today's news from Ford is the Crew Cab 4x2 model. It's unclear if the other versions of the 2017 F-250 will improve in a similar fashion.
In related but older news, Ford's aluminum-bodied F-150 scored well in testing when it was new. The 2015 model year F-150 SuperCrew received a five-star overall rating from NHTSA back in April of 2015.
The Ford pickups are somewhat newer than its competitors from Ram and GM. The Silverado 1500 went on sale in 2013 as a 2014 model year, and the Ram is older, having been introduced as a 2009 model in 2008. Engineering a vehicle to ace the latest crash test standards is usually a major goal of any generational change-over, and the rule of thumb is that newer vehicles simply perform better as the testing regimes get stricter.
Whatever the reason, Ford claims that this particular Super Duty snagged the highest NHTSA ratings ever in New Car Assessment Program testing. It remains to be seen if other versions of the Super Duty series can equal this feat.