Hey Tony,
We run a P2 - same unit as yours, but we miss out on the additional diagnostic features of the P3.
Anywho...I had cause to change the installation place of my P2. Where it was originally installed it was on quite a steep angle, whereas now its quite flat. Previously, on steep downhills, I experienced the same as you - van brakes would come on HARD. And in the storage yard, this little downhill pinch where we swing down to store the van, it would lock up the wheels on the gravel.
Since moving to the new possie, no probs at all. Application of brakes is much more progressive.
Not sure about resetting the controller or anything like that, but the pendulum/whatever it is that helps determine progressive braking seems to behave better for us when the controller is mounted flatter.
I've got another theory, but its just that - a theory - no proof. When going down steel hills, we actually WANT higher brake application than same speed on the flat. So the controller delivers. But with the controller mounted at a steeper angle, it gets sort of confused and thinks the hill is steeper than it is. And bang - brakes slam on.
I've been using the boost function - you might want to consider it. I have found with my current adjustment on the voltage, that boost setting 1 works brilliantly on the highway, then when I get into town I just turn boost off and everything is peachy. One button.
