To answer your question...No problems towing that sized rig with a Reg bed, SRW truck. Mine weighs 14,250 full and no problem with my Ford F350. No pushing, No bounce, No unstable feeling. good handling all around.
DEF is a non issue. A $12.00 jug every few thousand miles when towing. Not towing 5 gallons lasts to 5000 mile oil changes. I do believe it helps gas mileage. I get about 11 to 12 towing.
I can easily understand why one might not want to continue with a dually. But if I were you I might hold onto what you have for a few more years. I think you will lose your shirt for very little gain. And in fact you might feel some loss in handling without the dually. Many that never had a dually don't realize how well they handle heavy trailers.
I had one. It did tow well from a handling point of view. But the inconvenience factor finally got to me. And also the SRW trucks caught up with stronger suspensions. Couple that with the fact that we moved into a house that had a long narrow winding driveway. The longbed, long wheelbase, dually and the 102" wide trailer made it nearly impossible to back down our driveway. So I made the switch to reg bed SRW, and glad I did.
But I went from a 2006 dually to a 2012 SRW. So not really a good comparison.
But the apples to apples comparison, the dually is still the towing champion.