US Gear Unified Tow Brake

[RogerSwann]

Anyone familiar with this brake system.
I installed this on a 2016 F150 3.5L Ecoboost engine.
When I test by pulling the breakaway switch, the pedal does not move.
If I disconnect the brake pull cable, then it moves.
I started the engine while testing and the pedal moves. It is a "hard" pedal with engine off regardless of the aux pump running or not.
Is it possible this brake system is not compatible with a turbo charged engine?
I have connected this to 3 vehicles (Honda, Chevy) without issue. I have 2 of them so I swapped out the control box and have proper voltage and continuity on the wiring.
I'm baffled by the system works with the cable detached from brake pedal, but hooked up it does not seem capable of having the strength to pull the brakes. I get the feeling of a vacuum lock. I know this engine has undergone changes from an electric hydro boost (i think 2011-2014) pump to non electric in my model year, 2016.
I hate to spring for a new braking system, but cannot figure this one out.
Last time I called the support line, they directed me to an installer in AZ, I live in FL, not much help. I don't think the system is still made so the tech support doesn't appear to be interested or helpful.