Okay I was trolling, sorry! I know the numbers game the mfg's have to play. You say 3500lbs in the back? Yep did that a couple weekends ago, put 2 yds of top soil in the bed. Yes it dropped probably 3 inches but was no where near the bump stop.. I was praying the tailgate was going to hold up though because it was close to full.
Just as you believe the F250 is more truck than the ratings show many believe the same thing about the XD. There are many towing 5th wheels and toy haulers taking them over the GVWR and claim it does so with ease. I won't make that claim since I'm within the ratings with my trailer. The XD rear differential is the same one used in the NV3500 van rated at 5900lbs, only difference is the 6 vs 8 lug flanges on the axle.
What really surprises me is the weight of the F250 KR CC diesel, at over 8200lbs according to the weigh ticket I saw. That's crazy! That's 1300 Lbs more than my XD. I really thought Ford put this truck on a serious diet for 2017.