Transmission cluster panel gauge?

I purchased an RV and made one trip with no issues, but I have noticed while driving with no RV attached the transmission cluster gauge is staying on the far left and not getting to the center where it usually stays until quite a while as I am driving. I want to get this checked before I take the RV again. I read online where this model has the dip stick under the car passenger side. Should I remove the plug to verify the transmission level first before I change the filter? I used the tow/go with the camper and it pulled the hills really good with it engaged. I somehow think that the towing has brought the issue about. Your thoughts? Thanks