2025 transmission RPM issue - cruise control holding gear

[euromade]

Took my brand new 2025 on a road trip from Michigan to South Dakota with an aluminum enclosed trailer.   What I have noticed the cruise control tends to keep the truck in a much higher gear than it should have been in.   For the tranny to shift down one or two gears takes for ever, even going downhill.

I tried driving the truck at the same speed with no cruise control and it would grab  and hold a gear with 500 rpms lower with no problem.

if the cruise is set at the same speed level it would grab a higher gear and almost never shift down.  
In my opinion, 500 rpm is quite a difference as it keeps the engine and transmission running hotter.   On top of that it drinks gas a LOT more.

 

is there a known issue with the 2025 transmission as it relates to towing and gear selection?

thank you!

[Crazy Canuck]

How long have you had the truck?  In my experience (4th Duramax since 2021) it take a while for the tranny to 'learn' driving style.

[Rick_]

I just towed a tractor on a gooseneck on hilly roads between Great Falls and Roundup and I experienced the same thing.  On downhills, it'll downshift one or two gears, undershoot the cruise speed by 2-3mph and generally aggravate the driver. I expect the downshifts on uphills and that performance is acceptable.  Eventually I just cancelled cruise on downhills and played games with the exhaust brake to attempt to keep a constant speed.  This is not really an acceptable work-around as the you can feel the trailer pushing the truck and modulate this with brakes and the exhaust brake.  On level highway, cruise works perfect for the most part.  The inconsistent speed on downhills and downshifts that don't return are not just a 2025 thing.  It's also not just a GM thing, my buddies F350 smoker will do the same thing.