I know my DX3.0 came with the steering dual rate set at 70% for some odd reason, others have mentioned it too. I'd suggest checking that first, turn it up to 100%. Grip (thumb) button B, the middle one if I remember correctly, assuming that didn't change between the originals and the .0 versions.

Then set endpoints, both left and right. They should be able to go above 100% if needed.