I think it's just the reduced weight of the truck. My 2016 does it in the same way you describe. The 2009 never did it. Same trailer and setup.

 

Insane to think the 2018 is going to have a max rating of over 13,000 lbs. I barely feel safe towing 7100. These trucks run out of payload WAY before any limits close to that.

 

Does the feeling when you pass tractor trailers freak anyone else out? Maybe I am just overreacting to something that is fairly normal.

 

Try running a few pounds different between front and back, with the rears higher PSI than the front. Maybe drop your fronts to 40 or so, and see how that does.
That will make your front tires *relatively* saggier than your rears and produce more of an under-steer tendancy. You have plenty of PSI for those weights at 3040 and 45psi. I'm running 40psi with more weight on my front end right now.

 

Is 50/50 weight distribution on the tow vehicle desirable? Or should I loosen a link on the BlueOx? The truck basically sits level, the rear squats down about an inch and the front stays exactly the same height.

 

Don't know about weight distribution on the tow vehicle, but you have a LOT more rotational inertia (trailer) trying to push the back end around. If that wins, it has control of where the truck goes. If your rear tires are stiff enough (high load range and/or high pressure) you can get some control over all that.

If your rear end steps out, it makes the front steer the truck in the opposite direction: negative stability. The less you let the rear move, the more stable the truck gets.

That's probably why most recommendations I've seen talk about putting as much pressure in the rears as they'll take.

 

The new gen trucks are notorious for stepping out with the stock shocks. Replacing them is a MUST!

 

I tow a 18x8.5 enclosed trailer (probably around 5000lbs) at least 5 days a week down the highway at 60-70mph with my 2016 screw 4x4 20" wheels at 40psi with no problems. The trailer is smaller than yours but I don't use a weight distribution hitch either. I did install a hellwig sway bar and it helped.
My previous truck was a chevy 1500 z71 max tow and it did feel more stable than the f150 while towing before I added the sway bar.

 

The greater the speed diferential between your rig & the semi, the greater the push pull will be.
If semi is driving 65mph & you pass him at 75mph it will move u more then passing the semi at 67mph.

I tow the biggest side surface area trailer possible at 41.5ft long and 13'3" tall & I get moved around a little.
After awhile it comes natural to steer against the push pull and can normally make it a seamless process.

The other thing i notice is, the more i look at the trailer in the mirrors while passing or being passed, the worse it is. If i see a semi coming i move over in my lane and keep focus on the lane ahead and where i want to be in that lane. I dont feel its unstable, just different.

 

THIS is one of the MOST important things to know..and should be done in any type of vehicle on any type of road. Nicely said MagScrew!

Try drive a tractor/trailer on the main freeways near Chicago where you will have many lanes of rigs driving on what feels like 8' wide lanes...mirrors inches from each other. You just pay attention to what you are doing, not the others. The first time I did it was pure hell.

I once asked a FedEx train driver if his weaving trailers bothered him. He said..."NOPE, I never look back at them". He said two things....first, there is nothing he could do to keep them from weaving. Secondly, it would scare the heck out of him!!