I have a 2007 ES350 with just 105,000 miles. I have a very concerning problem. Recently I have had two instances where there was a momentary loss of power on the freeway accompanied by rapid beeps lasting less than a second. This occurred while climbing a fairly steep grade at 65 MPH.

I've also noticed hesitation while downshifting, but it's the loss of power that's the big problem.

There was no check engine light or engine codes.

The car is currently at Lexus service. I will not drive on the freeway until this is identified.

Any ideas? Do I need a new transmission?

 

That is a possibility or it could be a number of other things. However the cost of a used tranny from a different source is less expensive than a new one or rebuilt one from the Lexus dealer. You have to balance it against the value of the car. If the car is worth say $8000 but you have to spend $6000 at the dealer for a transmission or if lucky $4000 for a used transmission installed by an independent shop. Would you consider it a better investment to ditch the car for recycling value of $1000 more or less and put that money toward a different, newer, lower mileage vehicle? It gets complicated. What is the maintenance history? How long have you had it? What other problems has it had? What else has been replaced?

You can go to the Lexus drivers site linked below, join for free and enter the VIN of any Lexus you are considering to buy used and then it lets you see the dealer service history and find out if a dealer ever changed the transmission fluid. The site is a bit cranky and does not always work, so you may have to try a couple of times. https://www.lexus.com/My-Lexus/account/create-account

​​​​​​To see the service history at Lexus Drivers do the following:
On the page that lists the car whose VIN you entered there will be a line that states
Vehicle Health Report
Learn More - click this box
Then on the next page it will state
My Service
On the right side it will state Service History
View History - click this box to see the service history
Then it will slowly take you to a page you need to scroll down to see the service history
Each entry will be a line, click on the + at the side to see more about each entry

 

The car lost traction (pothole, standing water, ice...) and activated Traction control (beeping) which means cut the power. That is normal.
Maybe your tires are worn or old.