I had axle problems with my 2012 ST26BH - similarly equipped as your '07 with 3700lb axles, also with a GVWR of 7700lbs. I had it in for some other maintenance, and asked the technicians to look into some significant wheel twisting when I was maneuvering with the trailer. Ends up the axles were "out of spec" and were replaced by Lippert. I ended up with 2 5200lb axles now. I'm pretty happy about that - it was purely Lippert's decision to put heavier axles on the trailer.
2015 Sunset Trail ST28BH Reserve Package
2011 Ford F250 Lariat 6.2L V8 Crew Cab