Not a good gyro, I personally like the GA250 gyro and I am having great success with it on the 450 and 600.  In fact, it has performed better than my Futaba GY520.

You are in luck, I have the answer that you are looking for.  I had the HK600 belt drive and it has a known flaw.  The teeth on the belt pulleys are too shallow.  I am willing to bet  that you hear a weird sound when you punch it.  Well that is the belt slipping.  You can go two routes.  The first is to spend the money to convert to a torque tube.  The cheaper route is the go buy the Align belt gears.