My 2020 ES has about 8000 miles on it and has some hesitation under steady, medium-heavy acceleration or any other situation where the engine is under a higher load. It is especially noticeable in 3rd and 4th gear. The acceleration isn’t smooth or consistent. It’s hard to describe, but it doesn’t feel like the engine and there is no noticeable change in engine sound.

not sure what I should do about it. I’ve mentioned it to the dealer and they just say it’s normal, but I have a hard time believing that.

Don't believe what the dealer is telling you.

Is it behaving that way in SPORT, NORMAL or ECO?

It exhibits the same behavior regardless of the driving mode. It isn’t random or intermittent, I can reproduce the problem and predict when it will happen during driving.

Doesnt seem normal at all. Ask the dealer to ride with you in yours, then try another on their lot to see if it behaves same way.

I’m going to do that. No other vehicle I have ever driven does this. My wife’s Highlander is perfectly smooth.

Is this happening when you accelerate from a stop or when you are accelerating again from like 30mph? If getting on the gas from 30mph or so, it could be a lag while the tranny takes it's time going from a higher gear to 2nd or 3rd.gear.

It happens from a stop or accelerating from a lower speed as in passing someone on a two lane road. The issue isn’t during shifting, its during acceleration. It almost feels like the tires are slipping on the road, but without the sound or vibration you get when that happens.

Bad fuel? What with the pandemic, maybe not driving as much and old fuel in the tank? Look for vacuum leaks, loose battery connections and the like.

Defiantly not old fuel. I drive for a living so I'm in it every day. I've only had the car for about 3 months and already have over 8000 miles on it.

Have you tried observing whether the slip indicator light flashes when the issue occurs?

If it does that indicates the TRAC/VSC systems are operating to control slipping during starting or accelerating in slippery road conditions. Granted you haven't said you were operating in slippery road conditions but if something isn't quite right (e.g., marginal sensor, loose wiring connection, etc.) within those systems you might be getting a reduce power to the wheels reaction from the system due to a faulty perceived slipping condition.

While accelerating it is highly preferable to keep your visual focus outside the vehicle so the slip indicator light condition may not have been something that caught/catches your attention. You can also turn off TRAC/VSC systems (see the Owner's Manual for the procedure to turn both off) and then run a trial to see if that has any affect on the symptoms your observing.

That’s a good suggestion, although I thought of that already. No TRAC indicator and turning off TRAC and VCS doesn’t help.

I had the same issue on my 2019 ES350 FSport. When I complained to the dealer, they replaced the fuel pump and the difference was night and day. The car was so much more responsive.

The throttle response seems very dumbed down for me when in ECO mode. When I put it in Sports mode no problems at all.

By design.