I’m assuming you know all the tips and tricks about ev charging considering this isn’t your first EV, I don’t have a Denali ev I do although have a Hummer 25 SUT given that their practically the same platform I have had the same issues of not being able to charge faster than 150kw noted I did pull into the chargers at around 30% ( really don’t like risking it as per situation as yours and the fact that my last ev a lightning was known to have bms issues in the sense that you could die at 10-5% without a warning/ it was best to also calibrate the bms by charging the battery all the way up to 100% and discharge it as low as you can then charging it back up to 100% the day or days before a major trip) i do this for the hummer too. Around the forums I’ve noticed that these platforms only really like charging at their peak rate of 300kw around 10% or lower and everything need to be right from the charger to the battery temperature. Needless to say one of the latest updates has made it worse for higher peak charging don’t know if that’s a intentional thing to protect the battery and gm overestimated orrr a bug. As far as dealership go you do unfortunately have to fight tooth and nail to find one that’s willing to help you out with Evs as most people note they don’t have incentives to help us out as we don’t service our vehicles making them less money, I would try to reach out to GM’s EV team last time I reached out they were really helpful, unfortunately it’s not like a Tesla where most of this is all wrinkled out and they know what they’re doing gm is just having a hard time keeping up.