You can't get a 12000 lbs trailer, and pull it with a truck only rated for 10000 lbs and be legal.
From Virginia: I checked into this before purchasing my 10k# capacity trailer to be pulled by my 9.2k# towing capacity truck. I actually found the language in DOT code regarding the issue and it was very clear...the TOWED WEIGHT of the trailer is the defining characteristic. The rig must be weighed and compared to the GCVWR to determine if you are "in bounds".
You can't be ticketed for towing air. Defies logic. I'm not saying that some communist hasn't gotten this into DOT code somewhere...all I'm saying is that for me to BELIEVE this old wive's tale,
I want to see a quote or link, chapter and verse, to someone's state code or state DOT requirements.
Then I'll avoid that state like the plague.
2005 F-150, 4x4, Screw, King Ranch with 3.73 gears. ...What would YOU do?
My 2005 Eddie Bauer Expedition is very similar to your truck. Same engine and if you have the tow package, same optional gears.
I have loaded my truck to capacity (9,000# trailer) with bumperpull and WD hitch and it did OK. When you get that much weight, you start feeling the "wiggle" on the rear tires when pulling through a corner and need to put it in AWD to not slip around getting started on gravel.
I really like the engine and its wonderful blend between power and economy, but this type of load really is at its upper limit.
Honestly, I have no idea what you should do. I've given considerable thought to the matter and this is where I've headed thus far:
--IF I got a pickup to better my tow capabilities, I'd get a 1 ton diesel.
--IF I was changing to gooseneck, I'd get a dually.
--IF I stay bumperpull (which I will for the next 15 years, give or take), I'd stay single-rear-tire.
Unfortunately, circumstances demand an SUV for me, so I need to wait until they come out with the small-displacement diesels for me to make any change...think 3/4 ton Diesel Suburban...
My wife heavily influences our purchasing decisions, even on things that don't have any real impact to her. When all I had was my utility trailer, she wouldn't HEAR of me purchasing a diesel. "Stinky", she would say. Now that we pull a travel trailer for hundreds and hundreds of miles over mountain roads, she finally said it..."Honey, do you think a diesel would be better for pulling this?" "Yes, dear. It would." "OK, then. You need to get a diesel in your next truck."
And so it goes.
WHAT WOULD I DO? Probably, I would get a 12k# bumperpull trailer and WD hitch. I'd balance your tractor over the trailer wheels instead of over the trailer ball to help with your sag issues. I'd thusly use the rig until my truck was ready for replacement, then I'd get a 1 ton diesel.