How long can I drive car before I have total transmission failure? 2005 LS430

What is your question?

05 has 255k miles, replaced radiator, then started having shift issues. So I had the transmission flushed. Still having intermittent shifting problem from 3rd to 4th. My mechanic gave me an OBD device to clear the codes. I do that before driving, but the code comes back after just a couple miles. Not sure if this has an affect on the shift problem. I can still drive it normally, but it still intermittently doesnt shift and the rpms go to 3000 or 4000. I then pull over and sit for a few minutes...then start it up and it drives normal again. There are a wide range of pricing for this Solenoid C, so I havent ordered it yet.

What makes this problem better or worse?

It's worse when engine is cold

How long has your 2005 Lexus LS430 had this problem?

6 weeks