If you are using the 3GX with satellite receivers make certain that you have the tail rotor gyro gain control being controlled by Channel 7/AUX2 or you will not be able to control the gyro. Your radio defaults to using Channel 5. Fix that first.
The values in the Gyro Sense menu control the gain. I have my gain controls slaved to my flight mode switch (X9303, but quite similar to your DX9).
If the gain values in your DX9 gyro sense menu can go between 0 and -100 and between 0 and +100 then the negative values will put you in rate mode while the positive numbers put you in Heading hold mode.
If the numbers only go from 0 to +100 then numbers between 0 and 50 put you in rate mode (0=100%, 50= 0%) while numbers between 50 and 100 put you in heading hold mode (50 =0%, 100=100%).
If the status light is green the gyro is in HH mode. If red, the gyro is in rate mode.
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