I have just over 13,000 miles on my 2019 GMC Sierra Denali Duramax now, all has been OK until this trip. My fuel mileage had been increasing, etc. as the miles went on. This trip, my DEF usage has gone to 7 gallons every 1500+ miles, fuel mileage has dropped to 9 mpg (it had been over 12 towing), I don't get the usual DEF notifications. No 30% or 1000 mile notification, just an Action Required Now-engine will shut down in 500 miles. The power seems to be OK. I have taken it to a shop on this trip, they checked the system for leaks and said they make some ECM updates--it didn't change anything. I have a GM reference number now so I'll be taking it in when I get home. Just wondering if anyone has any info I can help the dealer with. Thanks.