The switches would only need to be changed if you changed battery types.
What I would try is this: Disconnect one battery and fire up the inverter, if it continues to have the same symptoms shut it off, and change the connected batteries and try again. If the symptoms are the same then the trouble is in the inverter.
I remember that mine (DR1500) had a sensitivity setting for load. This allowed it to "idle" at a minimal draw and only pull hard AMPs from the batteries as was necessary. This was a dial??? Near where you set the battery type. You may want to make note of it's current position and with the inverrter off run it from stop to stop a few times and then put it back to the original position.
If none of this works you may just have a defective unit. Before pulling it out and sending it in I would call Trace and see if they can offer any other troubleshooting.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato