[rohrmann]

Just a suggestion that should be a maintenance item, is get into your breaker/fuse panel and tighten all the connections, both the 12 volt DC and the 120 volt AC at the breakers, and any other connections you can see there. Also, all the connections where the batteries are should be checked for loose connections too. The fluctuation in motor speed can be caused by loose connections. You may want to disconnect from the AC power coming into the trailer just to be safe, and just be careful when tightening the 12 volt DC connections. If you have a battery disconnect switch, you can turn that off so there is no voltage in the panel if you are more comfortable with that.