Help! Slave Engine being Drug

Looking for Tips!  I have 2-f7 units. One A unit that is the lead engine with a PS2 3volt board and the 2nd A unit that has a Slave Board. We will call these B&O F-7's. The B&O lead unit works fine. When connected to the slave unit the slave unit is being drug. For testing purposes I pulled out my Pennsy AB units and had the same issue when having the Pennsy A connected to the B&O Slave. I replaced the male connector cable going into the B&O slave. The B&O slave then would work as it should. When again connected to the B&O powered it still would drag forward and reverse. When having the B&O powered connected to the Pennsy slave the Pennsy slave would work ok in when going in reverse but when going forward the pennsy slave would be drug. I had then replaced the harness in the B&O powered unit and well as the 10 pin wire and female PCB board. So powered has a new PS2 wiring harness to the PCB board and another new 10 pin cable that goes to the back of the B&O powered A. Other things that were tried were a new Slave board. Another PS2 3 volt board installed. Everything tried resulted in the same outcome of the B&O slave would be drug. One thing that I did find however is that when I would slow the B&O lead units motor that has the tack reader, or press down on the frame to slow the tack reader motor then the other motors would power and then turn and work properly.   For power I Have a Z1000 brick going into a TIU. I am simply stumped!  Any suggestions or things to try would be greatly appreciated.