I have a 2019 Sierra HD with integrated brake controller. I'm towing a 5th wheel camper with two axles and electric brakes on each. Behind the camper I'm town an ATV trailer with two axles, but only one of them has an electric brake. Towing either of the trailers individually there are no issues with the trucks brake controller to control the brakes on the trailer. But with both trailers connected the truck won't apply any 'juice' to the brakes. It does nothing - no brakes on their trailer. When I manually apply the brake controller it does nothing. GM is telling me the truck is only designed to handle two sets of electric brakes and if I want to handle 3, I would need to add an after market controller to control the 2nd trailer separately. I can understand that, but does it make sense the trucks computer/controller would not apply any 'juice' to the brakes when it senses too much resistance via the 3 sets of brakes? Has anyone had this issue? How did you resolve?