Slow Shifting Transmission When Cold

The Check Engine Light is on? Did you read the DTCs.

The second link has the answer, the first link says it is a known issue. It is times like this you need the Dealership or a good auto electrician.

Transmission won't shift to third until temp rise

ClubLexus https://www.clublexus.com > forums > 713188-transm...
Apr 1, 2017 - Transmission won't shift to third until temp rise ... The solution is to drive slow and keep rpms at 2.5k and 3k at max till the engine and transmission warm up.
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Owner of Lexus RX300 with 182000 miles. Recently the ...

JustAnswer https://www.justanswer.com > lexus > 3wsxt-lexus-rx3...
Aug 22, 2010 - Recently the transmission won't go into overdrive. Stays in 3rd gear like when you press the o/d button to do so. When car is cold (live in ...
1 answer · Top answer: Hello and thank you for using just answer! The check engine light is on correct?

https://www.google.com/search?q=Lexus+RX300+will+shift+into+overdrive+once%2C+and+after+slowing+down+it+won%27t+go+past+3rd+gear

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smell the trans fluid if it stinks its time to change, change the filter and do a pressure flush to make sure all bad fluid is gone.

Cold start circuit could be plugged with carbon. Throttle body may benefit from a cleaning. Or possibly the cold (warm up) valve.

you need 1 and 2 shift solenoid and the overdrive shift solenoid

A defective Throttle Position Sensor can play heck with shifting and that is about it.

the pump is inside.

You may have a case of morning sickness. in a transmission they are seals the are bad and leak fluid past them. causing a shifting problem when cold as fluid warms up seals swell and your pressures increase allowing a better shift.

Check to make sure the transmission has enough oil or put in new oil. It could also need a new transmission filter if that is applicable. Anything other than that and you are getting more expensive most likely.

yep motor mounts was my first guess

could be a cold start issue. there is a water temp sensor near the thermostat. when you start your engine first for the day it will show the engine to be cold and therefore the computer will do a 'cold start', meaning using more fuel. but this should throw a computer code. if you are not getting any codes from the computer then check for a vacuum leak. like the EGR vacuum line for starters. the egr should be closed when the engine is cold and open as the engine warms up.