Self-leveling Susp problem caused by towing?

[Ranger]

I occasionally tow 4500lbs with my '03 4.4. My self-leveling suspension is now acting up where one of the front wheels is pushed down 20mm or so. Is at the local dealer the 2nd time in a month for this. The first time they "recalibrated" the suspension. This time they are not sure what the problem is, but they want to blame my Prodigy brake controller, which is rediculous. But how can I convince them that blaming the brake controller is absurd?

It's worth noting that I've not towed since they "recalibrated" the suspension. So whatever was the immediate cause of this reoccurance of the problem, it wasn't towing.

The Prodigy brake controller is the recommended brake controller by most experienced X5 tow-ers. And BMW makes no specific recommendation for brake controller, at least as far as I've ever found. All the darn thing does is connect to a brake light wire or something.

So, how do I address this with the dealer?