Do the flush yourself and save $$.
Dropping Pan And Flushing Transmission
I absolutely believe the DIY way is much safer than a machine flush on a high mileage tranny. And it's easy and free (except for the fluid). EVERY instance that
I have ever heard or read about a flush ruining a tranny was with a machine. The DIY flush still gets as much old fluid out as the machine, but without any detergents or pressure.
I disagree with the statement about synth ATF. I flushed my tranny at 185K with Amsoil Universal Synth ATF and it's been great for 25K miles now and it's still nice and bright red (looked at it yesterday). Amsoil is rated for 100K/60K (normal/severe use). That's some good stuff right there. And yes, it says it's compatible with Dexron II and higher.
Also, the filter gets chunks of ATF in it (they look like little pieces of silicone/jelly). The write-up I linked to shows you how to clean the filter. However, I do recommend replacing the filter for 2 reasons. 1) it's a cheap part, and 2) the cork gaskets on my old filter were already pressed and formed. I didn't want to take the chance of not lining it back up exactly how it was before I took it off. If you don't, it won't make a good seal.
Another option is to leave the pan and filter alone. Drain what you can out of the drain plug on the pan, replace what you drianed with new fluid and then do the flush a quart at a time. This is almost just as effective, but you won't have to mess with taking the pan off or the filter. The downside is you wont get to inspect the magnets in the pan or clean/change the filter. If your fluid doesn't look too dirty now, I would probably just go this route.
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2021 Tacoma 4x4 TRD Off Road Double Cab Short Bed (my DD)
2017 4Runner 4x4 Limited (the wife’s)