Highway mileage will vary quite a bit in my experience, throw a regen in there and it can really seem "off." Your DEF use is also completely normal. I have no idea how Stbentoak gets 5000 miles on a 2.5 gallon jug. I might hit half that so ~2.5 gal every 2500 miles. And since DEF use correlates to fuel use, that is how much DEF I use for a lifetime vehicle MPG average of 23.0.I drove my 2025 Yukon to AZ and some strange things are happening. On my first leg things seemed to go well. I did get the super cruise to start working by going through a hard reset. It still drops out frequently even on the interstate. Super cruise did scare me a couple of times when traveling in the right lane and and passing an exit. SC will start to drift into the exit the correct abruptly back to the left and will go a little into the lane to the left before settling back into the proper lane. Im in AZ now and SC again is not working. I get the super cruise “ Hands free driving not available- No road information” message. I guess I need to do another hard reset. I think SC needs more engineering work.
On my swcond leg to AZ fuel economy sucked. On this 756 mile leg I could not get better than 22.1 mpg on all highway driving. I picked up the Yukon from the dealer new with a full tank of DEF. I now have 3876 miles on the Yukon and I got a display message that I only have 990 miles left in the DEF level. After that bad day the following day my diesel mileage went back to its normal 27.8 mpg on highway driving. Hope these problems settle themselves out soon. As far as Super Cruise goes I think I just had greater expectations from the advertised capabilities than I got.