Last night we had to go clean out our hog lease and remove our gear to satisfy the end of lease arrangement. Bad this was it rained saturday night ALOT, like 2" in a just a few hours
the 3 mile or so county road leading to lease is gravel( less than 1/4 inch pebbles) packed sand red clay pinestraw type surface. SLICK as owl snot in shady spots and then dry as cookie dough in the other parts so the stuff you pick up and toss in wheel wells really builds up fast on the cab steps, mud flaps, mirrors and rear bumper. the road in the lease is red clay, with a toss in of leaves, and some iron ore pebbles (slick and not supportive when wet).

I had just refilled the def tank and the range was 7000 miles .

so we get into the lease, download the hanging feeder and clean up our STUFF and leave. Mind you i was in 4h going in and really having lots of wheel spin and big chunks of red sticky flying all around.
leaving i was in 4l and locked the rear, made a huge difference, but still threw red sticky stuff everywhere, in fact when we reached the county road the stuff was so thick and built up the only place in wheel wells not cake up was about 2" around each tire. it was fun.
so we ran out the county road to the intestate and lost some mud, but not much
i get up to 77 and scan through the gauges and now my def reads 6000 miles to emtpy, praying for rain to wash off some mud...nope i had adobe bricks glued to the truck by time we got home.
dpf was still at 10%, not that it mattered. But i found it funny i used extra def playing in the mud for 6 or so miles

and 4l was fun in the slippery mode..it made the trip worth while. bulldozed through the crap

 

Sounds like a good time was had ! I love any reason to use 4x4, especially in mud.
My last truck (2020 Silverado 3500HD) would DING DING DING and say "DEF range to Empty - 1000 miles" usually about 20 minutes after filling the tank when hauling our trailer (7000 lb bumper pull)
Just for fun once, I pulled off at the next exit and tried to add DEF. The picture below shows the results - it took about 1/10th of a pint before barfing all over the place. I took it to mean when hauling, the truck would burn through all 7 gallons of DEF in 1000 miles. Get used to it was what the dealer told me...
Many of us were sold on the dealership salesman bs that "You'll only need to fill the DEF tank at oil changes" but that's just not true. It burns the stuff FAST these days to keep NOx in check when the engine is under load.

 

that looks like a baby threw up

yes i really like tossing a 8k lb truck through the mud, but its heavy up front and will plow if not on the throttle to keep momentum up.

 

DEF usage is tied directly to fuel usage. My truck uses noticeably more DEF when towing at 8-10 mpg than 14-15 mpg running empty. Slinging mud in 4WD I'm sure your MPG was way down so the DEF range probably recalibrated accordingly.

Unrelated to DEF use, but high RPM/EGT temps will keep your DPF filter cleaned out and run longer between regen cycles.

 

around 3K for the newer trucks with heavy towing. Goes through the DEF pretty good. I like that better than dumping fuel down the exhaust though.

 

I know my buddies cummins drinks DEF like crazy under heavy load. We did a 4000 mile weekend to eastern Ohio and back hauling a big box trailer loaded pretty heavy coming home west into some good wind. Truck was getting 8 mpg and going through 2 gallons of DEF every third tank of fuel or less than 1000 miles. .