Originally Posted by jdphillips
I am wondering how much different it would pull in the wind and through hills.
Probably not enough difference to be noticeable.
Gusting cross winds can more easily cause sway because of the additional square feet added to the sail (side of the trailer). But if your Equal-I-Zer hitch is not up to the task, then the fix is to invest in a ProPride or Hensley Arrow hitch.
My tow vehicle is a 04 diesel ford excursion which pulls my current TT with no problem. .
Your GCWR is 20,000 pounds, so you should be able to grab and go with any trailer that has a GVWR (max wet and loaded weight) of less than about 11,000 pounds. The additional weight might cause your X-Car to grunt more going up steep mountain passes, but your 6.0L diesel is a powerhouse that should make it with any trailer that weighs less than about 11,000 pounds.
Your primary problem with an X-Car dragging that much weight is hitch weight. Your tow vehicle has a limited GVWR of only 9,200 pounds, and by the time you fill it with family and stuff it may be close to the GVWR before you add the hitch weight of your TT.
With the wet and loaded trailer tied on and the Equal-I-Zer hitch set for towing, and with your 40-gallon stock diesel tank full of fuel, weigh your wet and loaded current rig on a CAT scale. Compare the weight on the two truck axles with the GVWR of the truck. If your current rig weighs more than about 9,000 pounds on the truck axles, then your truck suspension will be overloaded with the heavier trailer tied on. If you're less than about 8,900 pounds on the two truck axles, then you have barely enough excess weight capacity for the ~300 pounds additional hitch weight of the heavier trailer.