This is a forever truck for me so I do a drain and fill every oil change.
I use my rig pretty hard and its way too heavy so my oil change interval is 5k. When I got the truck at 120k it had a transmission fluid service at the Lexus dealership at 60k but I have no idea what that entailed. So I did a 4x drain and fill (62% new fluid) over about 1k miles.
Since then the plan is to continue drain and fills every 5k. I think a lot of you will think this is overkill but since the whole thing holds 12 quarts and I assume 60k is the fluid life, you only ever have about 77% new fluid even with a 5k aggressive drain and fill schedule.
Because I do them so often it only takes about 15 minutes and since I'm convinced the Valvoline is better in this application, it only adds 20 bucks to the oil change cost.
ChatGPT made this graph for me that tracks fluid health. This is after a 4x drain and fill at 120k and models out 5k and 10k drain and fill intervals (assuming 60k fluid life).
There is a way to pull the cooler line and drain 1 qt, then refill 1 qt, then drain 1 qt, then fill 1 quart, until the line runs cherry. However, I'm too scared to do such a change.