I felt a disturbance in the force.....
I'm going to say this first, save your money and get something better. Support for the 3GX is gone and is never coming back. The MicroBeast is awesome and is what I replaced my units with.
With that said, I know that money does not grow on trees. So....
First thing, connect that gyro up to a computer and get the software for 2.1, and put that firmware on the gyro. Yes, it is missing some features, but it is the most stable. You can get the software and firmware at the link below. Also, this link has some videos for the gyro as well.
Align 3GX Gyro | Rc-Help Forum
Part 1 will likely solve most of the issues you are having. You will need either a full receiver with the wires, or you will need some satellites. Since you are using a 6ch Tx, you really should use the full receiver as it will put the gyro gain on channel 5. If you run satellites only, it will put the tail gain on channel 7, which you don't have.
Let me know if you need further assistance.