I'm not too sure, someone on a forum grabbed the info from a TFL blog/video or something where they tested those models.
One surprising thing with my truck is there didn't seem to be any consideration for the massive exhaust tip hanging out the back waiting to be crunched. Damn thing is probably 4" diameter and isn't tucked at all. Only one company makes a DPF-back system that tucks the tip up near the bumper, and they want nearly $500 for it.