In the last few weeks I've noticed a shudder when accelerating, and it's pronounced when I'm climbing (I live in a mountainous area). The shudder is barely noticeable at low speeds but becomes pronounced at highway speeds. I've read it could be anything from spark plugs to cv axle boots. I'm not mechanically inclined so I'm at a loss. Curious for your thoughts. Thanks!

 

What year is your RX? How many miles are on it? Is it an F Sport?

As you said, it could be anything. I would first start by pouring a 20 ounce bottle of Techron Fuel System Cleaner in the gas when you fill it up. It works while you drive to clean out the fuel system and engine top end. That may help and it costs less than $20 at any chain auto parts store or Wal-Mart.
You could also just need an air filter replacement. It is easy to check and replace on the RX. And the same auto parts stores will have new filters.


Do you have a local trusted independent repair shop? The mechanical bits on the RX are shared with many other Toyota and Lexus models. This engine and transmission etc are shared with so many other models that every shop in the US has worked on them. Try Google and Yelp to find a local shop. Or use this database of recommended shops from listeners of the Car Talk radio show to find a good place near you. You can search by city and state. Then cross check the shops you like on Google for newer reviews.
​​​​​​https://www.cartalk.com/mechanics-files

 

Thanks for your thoughts! It's a 2010, not an F sport. About 113k miles. I'll start with the fuel system cleaner. I really appreciate the link as well. I live in a smallish mountain town and don't like to use the locals as they price gouge, so I typically drive into the more populated areas but haven't found someone I really trust.

 

I would first try draining out the old transmission fluid and adding new transmission fluid. If the issue goes away or is improved; then I would try another fluid change and go from there.

Poor performing Toyota/Lexus transmissions tend improve with only just a transmission fluid change.