2008 Dodge 3500 6.7 Dually has had 4 new MC and a brake booster, calipers and everything you can think of. The issue is that while driving the brakes are fine when serviced but when I hook to a trailer and apply heavy pedal they go to the floor and then I need to use trailer brakes to stop. I have thousands in trailer brakes and no one seems to be able to fix them....someone has to be able to explain. When they goto the floor I lose about 1 inch of fluid...