While it is not uncommon for manufacturers to add a few pounds, a 600(272kg) pound gain is a notable addition in matter of weight. The most plausible explanation for the additional weight would be the decision of the manufacturer to extend the availability of its heavy-duty payload package from the Regular cab and Supercab configurations with eight-foot beds, to the more popular Supercrew.
The configuration change beefs up the thickness of the frame rails, adds heavy duty shock absorbers, additional engine cooling and auxiliary transmission cooler. Taking a closer look, we notice that Ford did not boost the payload capacities for the 5.5-foot bed-equipped Supercrew, fact explained by the use of the same frame from the Supercab and the Supercrew allowing the carryover of the Heavy-duty Payload package, as repated by leftlanenews.com
Upgrading to the heavy-duty package also brings along the addition of seven-lug wheels, which have fewer aftermarket replacements available than the more common six-lug variants. Also worth mentioning is the fact that gaining additional weight capacity by adding components of heavy-duty nature will negatively affect fuel economy, acceleration and deceleration.