Ram owners. What gear while towing on highway?

I'm pulling similar weight with the Aisin tranny SRW. I always lock out 6th when towing and sometimes lock out 5th in the hills as the tranny tends to lug itself and hunt fairly bad. Lower gears would be nice when towing but would be a little low when empty running somewhere north of 80 on the freeway. The five useable gears for towing seem adequate, with a good gear for getting up and going when not hauling the 5er