What did you use for the hydraulic motor?There are some hydraulic augers made for tractors that requires way less flow to work properly. With one of those units, I can only see it working great, specially because down pressure can be applied versus the 3 pt ones and can also be reversed.
I built one for my homemade backhoe, that uses the auxiliary circuit with 4 GPM and works great.
Just a 200 CC Danfoss hydraulic motor. Straight to the auger, which I don't recommend, but I did it anyway at my own risk. It definitely needs a bearing support to take the axial load of the motor.What did you use for the hydraulic motor?