Not sure why you all need to set your brake control to 7 because I use 3.5 on my truck, though I am towing lighter. I learned to set my brake controller by running down the road around 25 mph then actuate the brake control. If wheels lock up on trailer, reduce setting on control until the TT brakes slow you without locking up. If you google setting trailer brake control this is what it would give you this procedure. The last thing you want to do is lock your trailer brakes. Adjust up or down depending on that lock up.