Auto trans has a hard time shifting to 3rd when COLD

When starting my engine cold (morning cold), my truck has a hard time shifting to 3rd. I'll run at 2000+ rpm in 2nd but won't shift to 3rd unless the engine has warmed up a bit. This problem just came up a couple months ago. Any ideas?

 

I used to be able to drive just fine even when cold. Never had to push such a high rpm

 

Mine does the same. I believe it does this to warm up the truck properly before hitting high speeds.

 

Mine does that from 1st to 2nd, and then 2nd to 3rd. After 10 minutes or easy driving it warms up and is fine.

 

Flush the fluid. The transmission is designed to do this to allow the engine to warm up, but as the fluid gets dirty the system doesn't work as efficiently.

 

The purpose of holding it in a lower gear when cold is to get the Catalytic Converter to operating temperature as quickly as possible. Cold start and warm-up are high emission periods and Toyota needs to get the cats "lit" ASAP. The owners manual mentions the delayed shift to 3rd when cold.

 

Mine with the 3.4 does the exact same thing.

 

my 3.4 auto does the same as well. after how many miles should tranny get flushed?

 

I haven't done a flush yet, and I don't know if the previous owner has (150k mi). I also haven't found a conclusive answer on whether flushing the trans fluid is safe or if it's better just to take the whole pan off.