Hope I'm not throwing gasoline on a fire, But . . . .
well you did!
I didn't mention this before, but my truck's rear bumper is designed for a towing weight not to exceed 10,000 lbs, and a tongue weight not to exceed 1,000 lbs. It has a ball that I use to pull my small flatbed trailer.
Where did you get this info from????? This is MOST LIKELY the specs if you are using a weight distribution hitch!!!
This below taken from: www.thedieselstop.com/forums/f32/towing-capacity-01-7-3-f250-177582/
I have no idea what your tow vehicle is, but this may help you understand a bit more about hitches!
Crawl under the rear of the tow
vehicle and find the embossed area with the weight capacities stamped into the frame of the receiver. The big number will probably be 1,000/10,000 WD. That means your max receiver capacity is 1,000 pounds hitch weight and 10,000 pounds gross trailer weight provided you have a weight distributing hitch.
So rule 1 is do not try to tow 10,000 pounds unless you have a weight-distributing hitch.
If your empty trailer grosses more than 3,000 pounds, and if your receiver is rated 10,000 pounds WD, then you don't have enough receiver for the job. So replace your receiver with a Reese or Drawtite Tow Beast class V receiver, which has a WD capacity of 14,000 pounds and costs about $300. Click here then scroll down to the Tow Beast.
If you don't already have a weight-distributing hitch for that trailer, then you can get one from any RV or trailer hitch store - even from a U-Haul store. Be sure you get one for a hitch weight of at least 1,000 pounds. Click here for one on-line source. Note that the "shank" is probably separate, but you have to have one that matches the rest of the hitch and receiver. The shank is the part that fits into the receiver.
The U-Haul hitch is mounted right below, and, as I said before, it has a max towing weight of 5,000 lbs and a max tongue weight of 500 lbs.
Your dry weight on your trailer is 4096 pounds, your dry tongue weight is 504 pounds, 900 pounds is nothing to put into your TT and you are already over your tongue weight......
My truck can haul 6,000 lbs in its bed, and it has oversized springs and shocks as well as a heavy duty rear axle. When I put 630 lbs on my U-Haul hitch, the truck remains level.
Glad you are level BUT you need a different hitch set up!!!!!!!!!
So what about physically tying the U-Haul hitch to the bumper hitch? Just for sake of argument, it would seem to increase the strength of both hitches by welding them together, wouldn't it?
?????

Just looking at alternatives of throwing away a $600 U-Haul hitch and replacing it with a hitch of higher capacity.
Who suggested such an undersized U-Haul hitch to you in the first place????? Based on the specs for your trailer, this hitch is not sufficient to "safely" tow it.