What transmission fluid do you use?

I'm wanting to drain and refill my transmission fluid and I'm not sure which kind to use, as I just bought the truck.
I believe my book says Dexron 3, but when I went to Oreilly's they tried to sell me some other stuff that we (dad and I) had no idea what it was and it was 2/3 more expensive. My transmission is the A340E, any help is greatly appreciated. Also has anyone needed to change their transmission filter? When I talked to toyota they said they don't do that.

 

D3 is what's used. I've used Redline D4 and Amsoil Universal ATF with out issue.

 

Valvoline maxlife stuff. Been using it for years without issue, its cheap and available everywhere.

 

I have no clue what is in it right now, is it alright to mix? Because I don't really want to completely flush it.

 

Amsoil

 

X2

Except I switched to valv full synthetic motor oil recently. I changed the tranny fluid shortly after getting my truck and just changed the filter too. Had a hard time finding the right filter. Turns out I had to get one for a year 2000 even tho mines a '01. May be one of those mid production differences. Idk.

 

I have a manual (3.4 2k2) and have had zero issues.