Vibration from 40-45mph
 

I have a 2009 es350, around 117k miles. Very recently started noticing a side to side vibration when accelerating around 40-45mph. Outside of this speed range, vibration stops. When not applying acceleration, vibration is not present. Have read a handful of forums that say the issue is likely cv shafts, but I also know these issues can occur due to torque converter failure. Any advice?

motor mounts, suspension parts, tire out of balance, lug nuts not torqued properly, wheel bearings , cv joints are a few things that come to mind.

More likely suspension or drive shafts than transmission if it shifts okay.

Almost impossible to diagnose online. Do not go to a dealer. Find a reputable local shop using Google and Yelp. These cars are not hard to work on as the same basic drivetrain design is used on several Lexus and Toyota models and every shop is familiar with them.

You can use this database to try and find a great local shop, but then cross check it on Google or Yelp for more current info. https://www.cartalk.com/mechanics-files
These are shops recommended by listeners of the old Car Talk car repair radio show.