'04 V8 is a sealed transmission with WS, the "horror" stories are mainly from improper fluid level after they've been flushed. That is quite a lot of miles with no known service, have you tried running the VIN in the Toyota Owner's website to see past records?
Toyota records show only timing belt and brakes done at the re-selling Toyota dealership at 130k. First owners had regular service at the delership. Second owner 90k to 130k no service records. Third owner did not have any paper work was recently divorced and thought it might have been done at a local independent shop.
The vehicle was and still is imaculate and drives like new.
One local dealership said they scanned it for a history of over- heating (I don't know how long the computer can hold this data) and viscosity. They said not to touch it adding that their parts delivery Tundra, an 04 with the same drivetrain, had 400k on it and never had the transmission flushed. The other dealship seemed like they wanted 400 dollars of money too badly and said it should be done immediately. I told them I'd service it myself. I do all my own service. I there for tires (yes sometimes you can get a raging deal from the dealer on tires) with one and the other dealer experience was for the open recall on the brake peddle chop and engine cut-off which I choose not too have done once I knew what it was.
I'm pretty certain that this runner was a highway commute vehicle most all its life and never towed. However the last 30k has been much mainly maintain conditions and I do some ""light" (2,300 lbs) towing. But the towing is also in the mountains. Still, I believe I drive correctly and have never come close to over-heating.
...so, I've ordered a case of WS off bay with the idea of doing 3 drain and fills more or less in a row. Here's where the catch comes in for me. I was debating 500 miles (yes 500 not 5k) intervals between drain and fills but decided against. Now, when the fluid arrives it's only four quarts (they made an"error" and are shipping the rest) or enough for one drain and fill, right? I somewhat believe in "signs" and took this as an opertunity for a reality check on the drain and fill intervals.
I know doing it all a one setting would be way less hassle but at the same time do not want to risk shocking the system by cleaning too much varnish or whatever off the transmission's workings with too much fresh fluid at once. I would like to get fresh fluid with fresh friction modifiers in there.
I guess I'll know a lot more once I see, smell, and taste the old fluid. Do those labs that do oil testing do ATF? Though, the flashlite test should tell me what I really want to know.
I do thank you for your input and I know it's a toss up or gamble either way: flush, drain and fill, multiple drain and fills, or do nothing.