I know what you are going through, I've had 6 regen in 808 miles. I'd drive the truck on the highway at 70 MPHs for 30 miles, exit into town and my truck would go into regen. Took it back to the dealer with 607 miles and on my 5th regen, they had the truck all day, drove her 44 miles on a road trip and jammed my rear seat center seat/shoulder belt. Said I was not driving her hard enough. Last week I poured in a gallon of DEF into the tank and now all of sudden my mileage is up and I haven't had a regen for 150 miles.....How is DEF connected to the regen process, fuel mileage not sure, or maybe my truck final burned out all the junk in the DEF after its manufacture?