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Well, in case anyone is interested, or runs into this later, it was the lift gate actuators, which are also the spring arms. They cost around 300 bucks, from the dealer, and was a fairly simple replacement, I think it took about half an hour start to finish.

Turning the switch off before it gets to freezing does not change the problem. Our 2017 Yukon XL has the issue as you describe above, and the console switch makes no difference whatsoever. For us, last year it worked fine, even down to about -5 F, this year, 28 F and it doesn't work, have to stuff the Yukon in the garage and let it warm up. Since we can't open it manually, which would be fine, its really hard dropping the kids off at the ski hill right now. Any guidance would certainly be appreciated before I start swapping out parts randomly

@cjpwalleye @SUB2018 Did you get any resolution on this issue? Our 2017 just started doing the same thing, if its 25 degrees outside, we are not able to open the tailgate. Turning on or off the power liftgate feature does not change it. In a heated garage it works fine. Very frustrating, i can't seem to find any info on this problem.