2nd Gen Transmission fluid service

Need help figuring out how to proceed, I know I can't be the first to ask this but my search returns either old threads and/or does not fully answer my questions.

I have a '07 Taco 4x4 Off Road V6 (5vz) with 138k miles on it, bought it used about 3k miles ago and have been slowly performing routine maintenance and changing all the fluids.

Transmission is a picky part on toyota's and most modern cars as well. It' takes WS synthetic fluid, everyone says to use ONLY WS fluid. Fine. Called the dealer he said he would not recommend doing a full flush service on this truck due to mileage and possibility of dirt/grime/metal shavings from the bottom of the pan clogging it up and eventually killing my tranny. I'm not OK with that. I want fresh fluid damn it!

It shifts ok, most of the time, every once in a while it will be stuck in gear longer then I would like then shifts with a slight jolt, but that is not the norm. I'm planning on driving this thing for a long time to come and would like this serviced.

Can anyone shed any light as to what your experience is with this, or if there are alternative methods of replacing it DIY or Stealer.

Cheers!