6000451 Antenna reduces my Speed.

Actually, I'm saying that the device with NO external antenna connections made has a 4x4 MIMO bandwidth internal antenna.  If you use the TWO external antennas ports, then you will be disabling the 4x4 MIMO internal antenna and limiting your reception to only the two external antenna you have plugged in and creating a 2x2 MIMO connection.  This will effectively reduce the receiver's ability to capture all signal paths by reducing total bandwidth by 1/2.  The only time you should need to use the external ports is when you are in such a weak signal area that you can't get a good signal.  By using the external antenna ports, you will gain a higher signal but the total data that can pass through those will be less than if you have a good signal using only the internal antenna.  It's a compromise that should be understood.  More signal doesn't always mean more data.  Think of it as a pipe.  You double the size of the pipe (4x4 MIMO) and you increase the amount of flow.  If your pipe is so long that it restricts your flow (weak signal) then making a shorter (stronger signal) but reducing the pipe size will give you some data but better than nothing.

Does the external antenna you're using have two TS-9 connectors coming out of it?  Are you plugging both into the bottom of the device?  If this is the case, then you will be in a 2x2 MIMO environment.  If you're only plugging in one TS-9 connection, then that is even worse.