The 722.6 has a internal speed sensor to determine the car speed. This signal is used for the electronic controller from Ofgear or PCS Due to rotational backlash it give’s sometimes shifting problems especially at low speeds you will get irregular readings and consequently strange shifting.
So it will be obvious that a ABS sensor in a front wheel will give the best stable signal .
All other solutions : from bad to good
1 ABS sensor if equipped on your differential
2 Integrate a sensor on your crown wheel inside your differential
3 Integrate a sensor ring + sensor in a rear wheel
4 Integrate a sensor ring + sensor in a front wheel
All suggested other solutions on the internet maybe also work.
Better solution? Let me know email@example.com