Changed my fluid out in January. Had the same thing happen. It was 20 degrees outside when I did it and not on perfectly flat ground so once the weather warmed up and I got it heated up it started venting out. All good now, though.
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I had same problem with my 2013 and after 3 trips to the dealer oh this and that. They finally rebuilt the rear end saying it was overheating causing the overflow. Hope this helps.
How many miles were on your truck when the dealer rebuilt the rear end?