Tekonsha P3 problem

On the advice of these forums, I replaced my cheap time-based brake controller with a Tekonsha P3. Braking is much smoother with it most of the time. I'm having a weird problem though, and I can't find anything with Google. Maybe I'm not using the right terms?

It shows a number that represents how hard you're braking. 0 when not braking at all, ~1-2 when lightly braking, and it would get up to 3-4 under heavier braking. I never saw it exceed 5, but I didn't watch it that long.

Every so often (it happened every couple stop lights as I was traveling through this city) those readings would suddenly double. Light braking would show 3-4, moderate braking 7-8. During this time the trailer was braking way too hard and slowing for stop lights was quite hard (the brakes kept jerking really hard and even locked up the tires once). The problem would go away after a few minutes. I did not change any settings during this time.

What could make the "gain" (if that's the right word) change so dramatically like this? I checked the boost setting, and boost was turned off the entire time. I didn't change any settings at all between when the problem started and it went away.

I had to finish my trip using my trusty old time-based controller, as I was a bit nervous using the new one under these circumstances.

 

I'd check the electrical grounds particularly between the truck and the trailer.

 

I have the Tekonsha Prodigy P2, and it has B, B1, B2, and B3 settings that you use according to the weight of your trailer. Are you using the settings? Sometimes I forget to change mine after unloading my flatbed and it brakes way too hard.