After 3 years and ~51,000 miles it was due.
OE fluid was slightly discolored but not burnt. It’s never exceeded ~180°F in the DIC AFAIK.

Used a floor jack against the transmission crossmember and a ratchet strap on the exhaust to gain the clearance necessary (~1/2") to work the pan free:




No TransGo reprogramming kit in the valve body this time. Black Bear tweaked the TCM to perfection:




Pan had a very modest amount of clutch dust and only a little debris on its magnet. Whew. :)
Cleaned the works thoroughly and blew out any residual lint with compressed air:




Replaced the OE filter with another AC-Delco piece. Same PN original filter was a NAFTA import, too:



Took about ~5.5 quarts of Dexron-VI to get it back up to the dipstick’s crosshatches.
Pumped and 'flushed' another ~8 quarts out through the cooler line (to renew converter's contents) until it discharged a nice fresh pink hue.
Got things good and hot then adjusted fluid level to sneak up on full after leak-check and test drive.

Budget an hour or so working at my old fart pace. :D

 

Source for reasonably priced GM-approved Dexron-IV ATF:

 

That jack idea is pretty slick if I say so myself.

Fluid looks okay still like you said and it never hurts to change it.

Sometimes at work we will just suck the fluid out of the dipstick tube and refill if requested. Mainly just because the filter labor is more and "should" be okay untill 75-100k miles.