2020 Silverado 50k miles, just got around to differential and t-case fluid swaps and found the rear diff was 1qt low. I recall reading someone else saying the same thing but never thought it could be wide spread so just filed it away in my brain. For what its worth, fluid was clean/not burnt. minimal material on the magnet. My truck came with the SU7 rear and SU4 front.
Moral of the story, maintenance your differentials if you haven't already.