I also had a problem with a 125A Gecko with SBEC, but the new firmware I got from Garret a few days ago has fixed the problem.
I have a Motrolfly 4320 (450 KV). At full throttle, the old firmware would cause the ESC and motor to lose sync really badly. Also if I advanced the throttle rapidly, it would lose sync. With the new firmware, I don't have any sync problems (at least on the bench). I didn't have any 6S lipos charged up, but with a Falcon 18x8 beechwood prop and a 6S lipo at 22.4 volts, I'm getting about 1500 watts. Everything was left on the default settings, except for startup power, which I set at 50%. The default setting for the startup power was a bit slower than I'd like.
I received the best customer support from Garret at Altitude Hobbies. He spent a lot of time with me trying to diagnose the problem since sometime in December.
If you are having issues with your Gecko send him email at
altitudehobbies@gmail.com. He will take care of you.
John