I know a lot of people who have the same truck with the same transmission I have (4R70E). Between all of them it does not seem to matter. I change mine every 30k and have had no problems, but I only have 108k miles. I am the hardest on my truck. I dirve it hard unloaded, but most of the time it is towing or hauling something. One friend has 250k miles on his and has never changed or flushed it. He tows with his a lot. Another friend never changed his and had the transmission rebuilt at just over 100k. One of my friends changed his every 30k and ended up replacing his at 150k.
My moms new Jeep only requires a transmission flush at 120k only if the vehicle tows a trailer, is used in the desert or other off road conditions or is used as a delivery, taxi or police vehicle.
The Jeep service manager said synthetic fluid, and better filters is a big part of why most manufacturers don't require a flush anymore. He added that in his personal opinion, if he planned to keep a vehicle until it rusted away, he would replace the fluid and at about 120-150k just to be safe unless he had the lifetime warranty.
I am sure that is because they get almost $200 for a flush and the deductible for the lifetime warranty is only $100.
I usually follow the schedule for vehicle I buy new, But for used vehicles I don't change it. The old saying "If it has never been changed or if you don't know if it has been changed, Don't change it unless it already has a problem" (which I know in general is really not true) Twice I have had a transmission fail after changing the fluid on higher mileage vehicles that I didn't know the history. Once on an 88 GMC and once on a 91 Caravan. They are the only failures I have had besides the shift solenoid on my current Focus.