When you "modified" the "TV Antenna Amplifier Plate", did you make sure the coax that's connected to the Tailgater bypasses ALL the circuitry on the "TV Antenna Amplifier Plate"? Otherwise, the TV Antenna Amplifier Plate" may block power (completely or partially) from the Dish Receiver to the Tailgater. The coax from the Tailgater to the Dish Receiver accomplishes two things: 1) it passes the satellite signal, and 2) it allows the Dish Receiver to supply power to the Tailgater.
It's best to not have any connectors between the Tailgater and the Dish Receiver to reduce signal loss. However, it should still work with connectors--assuming you've got good, solid connections.
It's possible some of your connections/connectors in your TT are faulty/intermittent, and/or the coax from the Tailgater is not completely bypassing your "TV Antenna Amplifier Plate".