New 2500 owner with questions

[Utopia]

New to the site but have been reading a lot and I have a question.  In recently picked up a 2014 2wd regular cab 2500 with a 6.0l v8 and a 4.10 rear end.  Vehicle has about 70k on it and has been well taken care of.  I have noticed when it’s cold that the transmission really whines in first gear the first time it shifts.  I know the whine is a common problem but mine will disappear after a minute or so.  Even after driving it, if it sits for a short while it’s the same thing.  It seems to shift fine and everything just a whine and seems, to me at least, to be a bit sluggish maybe.  And then it’s fine with no issues. Not sure if it’s just cold? Or maybe fluid is needing to build up or something?  No error codes or anything. Anyone else experience something like this?  Should I have it flushed? Thank you.