I installed my P3 last week, and picked up my 17z this week.
I have yet to do the above mentioned 25mph test.
I was set at 2.7 the only time I towed it, and it seemed like I needed to bump it up. I'm guessing I should actually do the test next time I'm hitched up?
Seems odd to "hit the brakes" at 25mph though. I guess just make sure you are on a quiet street with no one behind you...