This only happens under these circumstances. Tow boat to lake, no issue. Tow boat home, which is on a hill, no issue. Put rig in reverse to back boat down driveway and rig stumbles, rpms drop, then “service brakes” message comes on. No stored codes and new pads, rotors and front calipers. I’ve towed the boat for years without this issue. Something’s not right. No issues while not towing. Thanks all.