I know the FSM has tranny fluid drain/fill every 15k, but what are you flushers doing? I do a full flush every time, using the vehicle to pump things out 1 qt at a time. Could you then extrapolate to 45k? or longer?

I exchange the all the fluid every 50K or so and replace the screen filter, clean the magnets and use an aftermarket gasket. If the filter and magnets clean, I may exchange just do the filter every 100K. The main thing is to get the fluid out and have the fluid at least restricted as possible. I use transmission to pump the fluid out but at the time. I pump the fluid back in via buckets. You can see the method on my signature.

Nothing wrong with the spill and fill methods as well. This only gets about 1 gallon at a time though.

Try your best not to run the Transmission pumps dry though as that is not good for it. :-)

There is the opposite view that old tranny fluid helps the tranny.
This is why 60,000 interval Toyota recommends to do a drain and refill when in severe service.
Lots of Toyota experts do not recommend a complete tranny fluid change.
I think I will follow the 60,000 mile drain & refill for my and my daughter's SR5s.
I do have a Scanguage 2 that allows monitoring tranny temp. I do not tow, but I do fast drive CA mountains in summer with air temps over 100 F.
I shift into S4 when I hit a up grade and the tranny temp drops fast from 200 to 180 or lower. But Most all my driving is town and freeway.

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I did a full fluid flush when I did my shift kit install. Run it and drain 2 qts, refill etc until clean fluid came out. It had never been serviced before I bought it and now has over 245k miles and shifting and driving like a champ!

Every 15,000 miles? When did that become a thing?

maybe i'm misremembering the service interval. I thought 15 was in my head. maybe it said 30, idk now. I too have a scangauge. I think i actually flushed it last year or maybe 23 i have the log in the car and its freezing outside so i'm not getting it lol. i don't mind changing it under 60k it's only 3 bottles of tranny fluid and maybe 30 minutes of my time thats worth the life of my baby.

I do a pan drop every other change. I got nervous about this bc just before the last change, I shuttered to a stop driving to work. Shop didn't find anything wrong. I thought it might have been fluid bc i was near the 60k timeline and after i flushed it, never happened again. so...i don't know

Ive got about 20k on my last full flush. I also run a magnafine filter. Did the flush at about 230k,(would have to look it up) and have had no problems. This is the 3rd 4runner I have done full flushes on, all over 200k with no issues. I do mine like many others, pump some out, fill some back in.. 3 or 4 gallons

I think the old style power flush machines caused issues in many cars

How often you service your fluid is dependent on how you drive your rig. If it's a flat-lander grocery-getter, the fluid could literally last 100k miles. But, if you drive at all in the mountains, the life of the fluid goes way down due to the temps you'll be attaining climbing grades. As the temperature of the fluid goes up, the effective life expectancy of the fluid goes down.

For people like myself who do drive in the mountains and go on 4wheeling trips, I believe a complete renewal of the fluid should happen every 30k miles. But, instead of renewing the whole capacity at one time, I choose to do a drain and refill every other engine oil change, which comes out to a drain and refill about every 10k miles since I perform engine oil changes every 5k mile intervals. Drain and refills are a dilution process (adding new fluid to old fluid), but it works really well to keep your fluid in good shape.

There is no need to drop the pan on these transmissions unless you're just curious about the health of your transmission because you bought the rig used or your fluid was really black and in bad shape and you suspect the filter might be blocked up with deposits. A transmission that has been taken care of will not build up significant deposits to block up the fine mesh metal filter media in the filter. I've cut one apart, and the media was probably around 95% unblocked. So, for those taking the time to drop the pan to clean the magnets and replace the filter, I do believe you're wasting time and money.

A thing to do to guarantee you'll never have to worry about the trans filter becoming clogged, is put a Magnefine in-line filter in the trans cooler return line. Those filters are rated to last 30k miles. I replace them every 20k and it's a hell of a lot simpler than going through the pains of dropping the pan and cleaning off old FIPG off the pan and transmission.

I have a habit of "spill/fill" on every engine oil/filter change. As stated, about one gallon comes out with this method.

Aisin transmissions are pretty tough, rarely do they die from flushing. Now a ZF or a 4L60E? Have a transmission rebuild budget in advance in case it doesn't survive the flush. That being said an A340 with regular service shouldn't need a flush. I wouldn't dispute after 20 years that a pan drop to clean the magnets and replace the filter is a good idea though.

My trans maint. has been. Covers both ends of a sort.
96Red 374k mi never dropped pan imagine it due, did 3 4 qt D&F 100 mi interval, then every 35-40k+-,
Put in pint of SeaFoam Trans at service interval the last 2-3 times, shifting great when totaled.

Replacement 01 @198K questionable service been a different story, 01-02 340 has its quirks worst of series.
Did D&F as above no SeaFoam, good 15k+- mi. Trans started wining when temps in teens then wining at 50*F+.
Did another D&F no bueno after 5k or so, so dropped pan magnets had mud no metal on filter was due not real bad.
Did fluid exchange then dropped pan then topped off, cured wine above 50*F not in teens 6 mths later. Fug me.
As last ditch effort before diving in as an experiment put pint of S/F in. When teen temps returned no wine on 3rd winter.
Trans is "knock on wood" feeling more reliable how it's shifting since I bought it.
Not hawking S/F what I chose. Have found who to do rebuild in mean time.