Cobra Trailer Brakes

I had similar results after a long down hill drive that lasted maybe 30 minutes. I was down shifting, but ran about 40 mph. As I gassed up I checked the hubs and they were alarmingly hot. Didn’t want to keep my finger on the hub more than a second. After driving for another hour on level ground, they both were just warm. I concluded it was caused my the down hill run, where the surge brake was being applied because the tow vehicle was slowing down due to down shifting. Nothing else to the issue for the next 5 years.
Hope this helps,
JJ