Trans fluid change on my 2007 suburban with 320,000 miles.

Some mis info here, but good advice on the fluid change.
Honestly it’s flip a coin. I would change it. If it really is original trans with those miles it doesn’t owe you anything and I’d be surprised to see it last much longer.
If I wasn’t towing and just driving it around town I’d be apt to leave it alone but for work duty or long trips, you’re gambling with those miles anyway. Might as well give it the best chance for survival.