Troubleshooting Flight Controls - New Build

I just finished my first Quad.

Ardupilot 2.6
610 KV motors
12x4.5 Hobby King Slow flight Props.

My issue is the quad has a slow (about 1-2 CPS) oscillation. It will fly level, but hunts to maintain it. The oscillation rate is stable. It is excited by application of power, and dampens as power is reduced.

If this was the tail on a heli, I would assume the gain on the gyros was too high. I tried adjusting some of the gains in AMP planner, but it did not seem to have any effect. Where to start?

Is there a trick to get the values to transfer to the autopilot?

The only other issue might be the props…they are pretty flexible.