had mine flushed at 30k mi. will change filter at 50k mi. if someone like me, who only tows on rare occasions, trans temp stays low than recommended change is OK... but if someone is hard on there's towing a lot, racing lot, then change is needed more often depending on what the fluid looks/smells like and how the trans performed
my 2 cents is. If you buy a vehicle brand new, change the fluid as recommended in the manual, or every 35k-45k like rivereye said. If you buy the vehicle used with over 100k, I'd be worried bout changing it. If it had never been changed before, and you change the fluid, it could cause problems. Don't ask me how it can cause problems, just everytime I've seen it changed for the first time after 100k, problems arose fast, maybe it's just coincidence. And for me when the tranny burns up, gives me an excuse to build it bulletproof. Of course it would burn up at the worst time. i voted to change it, i'm a walking contradiction.
2007 2500HD Silverado 2WD Regular Cab 6.0 6-speed auto, Super 44 Flowmaster, Blackbear Performance Tune. As of 09/01/2014, motor is shot. rebuild under way.
There are horror stories about transmission fluid changes... but those are mostly isolated from what I have seen over my 2 years on the forum.
I say change at regular intervals, even if it has over 100k miles on it.