2005 Tundra Transmission Issues

My 05 tundra with slightly under 140k miles is having some issues shifting at highway speeds. The main issue I am having is that the transmission will shift normally 3 times when accelerating, but after that the rpms just keep climbing. At 55-60mph i am looking at 2500-2800 rpms, whereas when it worked normally I was right around 2000 if not under with those speeds. This would happen for anywhere from a few minutes to 15 minutes then shift normally. In recent months it stopped happening consistently altogether and shifted completely normally. This past week, it will not shift at all at highway speeds. This problem seems to come and go over the past couple of years, though until now it would always eventually start shifting normally. Some other things I have noticed: when cold, it takes a bit to shift out of 1st, and I may have to rev the engine a bit for the transmission to shift into second. The transmission fluid was a bit low despite having it fully flushed and filled again about 1.5 years ago, so I filled it and still experience the same problem. Has anyone else experienced this, or have any idea what the issue/fix could be? There are no codes for the solenoids. Hoping it isn't a full transmission replacement.

 

Late lower-gear shift when cold is typical. It's one of many quirks/issues mentioned here: https://www.tundras.com/threads/so-you-wanna-buy-just-bought-a-1st-gen-tundra-eh.115928/

Have you followed the standard procedure for sealed transmission, to bring it up to operating temp, and confirm fluid level once there?

Have you checked to make sure there's no coolant in your transmission fluid, or vice-versa (pink milkshake)? That's another one of the issues discussed in that thread.

 

Regarding the late lower gear shift, that is good I suppose, it is not a huge deal for me, it generally takes less than 100 yards to operate properly. I did check the fluid level at operating temperature. The transmission fluid that was in the transmission seemed perfectly normal to me. When I first started having this issue about 1.5 years ago, I had the fluid flushed and refilled, and that fluid also looked normal.

 

Hmmm...did you use Toyota WS fluid?