I had this kit a couple of years ago and don't recall having that problem with the controller. I'm sure I was reaching 15 mph on levels 3 and 4. I only used 5 on the steepest of hills. I also got caught out by the hub width but I didn't bother redishing the wheel. But getting the wheel in and out was a bit of a nightmare. I had the rack kit and my bike was not very stable with all the weight so far back and high. I sold it and bought a Wisper 705se instead.
How fast did it go in levels 1 & 2 before cutting off?