I have a similar issue with my 2007 RX350. Intermittently usually after removing my foot from the gas pedal and changing lanes in 25 to 35 mile an hour traffic I will put pressure
on the gas pedal again to accelerate and the transmission will slip into gear.
I reported it at the last week with my Lexus service department and asked them to check the transmission fluid to see if it smelled burnt. They said it did smell burnt and that there were small metal particles in the fluid.
I only have 49,400 miles on the car and have done all my services at a Lexus dealer. The service advisor and the mechanic that checked the transmission out recommended doing a
transmission flush for $300.00. They checked for software error codes but there were none.
This actually seemed to be a minor problem when I first noticed it and it only happened once in a while. Now it is a surprise $300.00 problem and my Lexus dealer is not treating it like it is a serious problem that they want to consider taking care of under warranty. Now I have to hope it finally fails within the 70,000 mile warranty or set aside and extra $4000.00 if it makes it past the warranty period and fails.
I would like to warn other Lexus RX 350 owners to be aware of this seemingly small symptom that could be the start of a serious transmission problem. I had the same symptom on my previous vehicle, a 2005 Toyota Highlander V6. When I reported it to my Toyota dealer after I found some information on it on the internet they acted like it was TOP SECRET and would not discuss it with me but gave me an 800 number to speak with a specialist at Toyota of North America to get authorization. It needed a software update.