Use your manual button on the brake controler. That is what it is for. As you go down the hill go slow and easy one foot on the truck brake, one hand on the steering wheel and the other hand squeezing the manual brake button as needed to use the full braking ability of the trailer as you go down hill.
I once had an Isuzu trooper that had 4WD. I pulled an 18 ft 2800 lb TT that I would keep at a friends house during hunting season. I brought my camping gear up in a separate utility trailer when I hunted. I had to cross his private pond dam make a slight curve then go up a very steep hill to his house. When I picked up the trailer the first time to pull it down the road to my dads property to camp while hunting. It was pretty scary the first time I went down the hill since if I didn't make the curve right at the bottom of the hill I could go off into the water or worse a 30 foot drop off on the down stream side of the dam.
I applied the Trooper brakes while I applied the trailer brakes with the manual brake button as I began going over the drop off. I let up off and applied the trailer brakes as needed and didn't have any problems at all. This was on dirt and gravel. You should be better off since you will be on concrete and asphalt.
Any time I was on country back roads with short steep grades I slowed down as I approached and grabbed onto the brake control and applied the trailer brakes manually when needed for extra braking power as a precaution.
