I go by my owner's manual. If you don't have one your Ford dealer will have info where your truck is new enough. I would not exceed tow limits even with helper springs or other aids because the issue is not just how much the truck will pull, but how much it can stop, and how it can handle in an emergency maneuver. brake controller or not, if you exceed the towing capacity of your vehicle and are in an accident, there may be trouble when they find out you could not properly control your vehicle because you exceeded what you were supposed to be towing.
Mine is a 4x4 and weighs about 4000# alone, with the stuff I usually carry in the back. My gross combined vehicle weight rating is 8000# but driving with that much, and I have, is not pleasant. Flat smooth roads help, but be conscious how your weight, load, balance, and such. I was living out of my travel trailer attached to the back of my Ranger, so have some experience with towing.
If the trailer tongue is too heavy it makes the front wheels lift off the ground some. Bad for steering and for tires. If the back end of the trailer weighs too much it lightens the front but causes sway. The load needs to be balanced and the tongue weighs what it weighs. A weight distributing hitch spreads the weight between the front and rear axles but costs more and you still should not exceed GCVWR.
I am sure others will tell stories of having hauled a full 7000# mobile home 400 miles down the highway with no problem but I would not have done it for safety reasons. Your motor will pull more than your truck safely can.
My trailer weighs ~2500# fully loaded. A little less but I figure that for safety. At 6500 I am well below the 8000# GCVWR and it is comfortable. I know you are towing with a destination and won't be leaving it on there but keep in mind the things about tongue weight, load balance, liability, safety. I would imagine you would be rated at at least 8000# GCVWR and probably 3500# on the trailer, though that may be with a weight distributing hitch. What does your owner's manual say?
95 Ranger Styleside SWB 4X4, 3.0, Auto, 4.10, 145,000 Miles
Century Cap, BF Goodrich All Terrain 30x9.50's, Reese Hitch, K&N Air Filter, Taylor Wires, Splitfire Plugs (I have had good luck with them), Bed Mat, Upgraded to factory alloy rims from "argent wheels", Cat, Dynomax Cat Back, Additional Battery Charging System, Transmission Oil Cooler, Grizzly Grill/ Brush Guard, Hella 500 Amber Fogs, Chrome Diff Cover, Nerf Bars, new bumper.
Upgraded to NH registration from Mass (Best upgrade!)
OEM Tube Rear Bumper, Tow Hooks, 31x10.50's, Larger or Additional Fuel Tank, Locker