Living in HI, guess you can't easily take a cross country road trip with hours at 65mph or higher!
If you're not having Tranny shifting issues, with ATF bright+clean red
& at proper level on the stick after warm up, I'd not worry about it.
Don't believe there's a way to drain the 3~4qts in 5r55e TorqueConvertor, short of removal+disassembly.
I would try to get vehicle to highway speed for a few minutes once a month, to keep the "arteries" clear.
With the V6~4.0L~SOHC Engine + 5r55e Tranny I've got here,
Tranny service is part of routine maintenance,
so I handpump+refresh ~1qt of MerconV fluid at the Tranny DipStickTube
along wth the Engine Oil+Filter change every 6mths Fall+Spring.
Also handpump+refresh ~1/2qt of MerconV at the Steering Reservoir,
& handpump+refresh the DOT3 fluid at the Brake Reservoir.
Doing a Tranny Drain+PanDrop+FilterChange every 6Years\67kMiles with 6~7qts of MerconV Drained+Refilled,
I figure this routine is equal to or better than a onetime flush of the total 10~11qts,
keeping it on a schedule with minimum"trauma" to Tranny internals.
I've read some commercial shop Tranny flush machines may cause more problems than they solve.