Haven't towed with mine yet, but have made two checks under normal driving to and from work and trips...first check netted me 1350 per gallon of DEF, second check netted me 1190 per gallon of DEF. Will be towing 5er from WV back to our home in NC Saturday after next and should get an idea of how much I use on a tow trip through the mountains.
On Edit: I got out my 2013 Diesel Supplement and the short version reads like this
DEF Low Refill soon..Message will display accompanied by a chime.
Speed limited to 5 mph in XXX mi Refill DEF, need to add up to 2 gallons to get rid of message and more chiming.
5 MPH Max Speed on Restart, Long Idle or Refuel Refill DEF..This will continuously display when counter reaches zero. Only be able to do 5 MPH if engine is turned off and restarted...Add up to 2.5 gallons to DEF tank to avoid vehicle operation of only 5 MPH and restore vehicle to normal operation.
* Minimum of up to 2.5 gallons, (9.5 liters), maybe required to restore normal vehicle operation. Although the vehicle will start normally and can be placed in gear after the message has been initially displayed, extreme caution should be utilized since the vehicle will only be capable of maneuvering at a max speed of 5 mph.
hope this helped to answer any questions about the Ram's information on DEF