I don't have an answer for your problem, but will share my experience with you. I had a 2010 F150 and pulled a Heartland TT. Same exact axles as your Cougar. I was also displeased with the axles. As for the braking issue. Our F150 worked flawless with the Heartland. And I could lock up the brakes on the TT.
On to the next part. Upgraded trucks. 12 Ram 2500 CTD . Same TT. The Ram TBC wouldn't even come close to locking up the TT's brakes. Faulty TBC. Replaced with just 1,000 miles on the truck. Still wouldn't lock up the TT's brakes but did work better. I also adjusted the TT's brakes during the Ram TBC fiasco. It wasn't anything to do with the TT's brakes, just an inefficient TBC.
On to the next part. Traded the TT in on a 13 Fox Mountain 5'er. Now the braking problem is the exact opposite. Brakes really grab when slowing. I have to turn the gain down to 2 in town and back up to 5.5 on the road. Backing up is worse. The TBC won't let go of the 5'ers brakes and they sick for an extra second or two. Really annoying.
My point to all of this rambling is maybe your TBC isn't working properly. You should be able to lock up those brakes based on my experience with the same axles and a similar weighted trailer. I always thought the Ford TBC was the smoothest TBC I had used. And prior to that It was a P2.
Just read your last post. Same exact scenario as mine. Sounds like maybe we both have brake issues and not TBC probs.
