Hi guys,

After a lot of reading and going down rabbit holes regarding ATF here, I reluctantly need to post for a somewhat straight opinion on my ATF.

I bought a 2001 2wd with 188k miles. What ATF is inside is totally unknown, and was overfilled. That being said the truck seems to shift fine. I did a transmission pan drain and a radiator/hose drain of ATF in the process of changing my radiator out, so I'm now short on fluid. Here comes the hard part:

Not knowing what fluid is in there, what is the smartest or safest choice?

1- Top off to factory levels with new Toyota T-IV, which I already procured but am now getting cold feet about mixing with whatever is in there. Perhaps without reason.

2- Top off with Valvoline Maxlife Synthetic, which I would have assumed is a no-no, but then again who know what's in there, that could even be synthetic.

3- Do a full "flush" via radiator line drain and topping off while running the engine, using Valvoline. In this case I'd have all the same ATF in the car, but I read about risk of transmission slip vs the pan drain method every 10-15k?

Thanks in advance! I don't want or mean to ignite a debate, but am hoping one of these is somewhat clearly a "safe" option