Performance issue

Hello,
I bought my 2015 4Runner with only 26,000 miles two months ago from original owner. It is very clean inside out.

I posted concern previously about how sluggish it was upon acceleration so I took it to my mechanic who suggested changing the oil again and he did using Mobil 1 0W-20W full synthetic. The acceleration improved at first then few hundred miles later it felt wimpy and sluggish again now at 27,500 miles.

The overall driving performance of my 4Runner doesn't feel like it has only such low mileage it feels like an older truck. Before buying it I test drove other 4Runner at dealers, about three of them. All of them were previous renters with around 40,000 miles between 2016 and 2017 year model. Each drove much smoother than mine.

Could there be something wrong with my 4Runner being a 2015 model? Perhaps it was not maintained properly by previous owner and sat for a while with no oil change considering the low mileage? Is being a 2015 model a factor for this low performance or is this how a 2015 drives? Is there additional maintenance that I need to do?
Please let me your thoughts.
Thanks, Mike