I recently bought a new 2014 Ram 2500 SLT four door 4X4 Diesel six speed diesel. I think they all come with the 342 gear. I also have a 27 foot travel trailer aprx 8000 lbs. My question starts with when not towing I average around 25MPG. When towing at highway speeds 70MPH while on flat land with cruise and tow/haul button on with exhaust brake on. It feels sluggish, Motor running at 1500 RPM's. It has plenty of power but just seems to run better if I put it in 5th gear, motor at around 1800 RPM's. Mileage drops to around 13 MPG. Trailer is 11'5" feet tall. What gear should I be towing in and should I be using the cruise control? Also does the mileage sound correct. BTW I am a newbe to this site although I have driven many Dodge diesels towing horse trailers. Thanks in advance