2019 Hyundai Ioniq - Transmission feel

When getting on the expressway and accelerating to 60-65mpg, the car seems to get stuck in the 4th and 5th gears refusing to go up unless I let up on the accelerator, which is difficult to do when you’re merging into expressway traffic from the left lanes where I live in Wisconsin. The dealers can’t even put the correct oil into the car, rotate the tires correctly, or do anything I pay them to do, even though I have complained. The Hyundai service dealers have not demonstrated competency in Madison to service these vehicles unfortunately let alone understand what I tell them is wrong with my car.
Stay away from the Hyundai altogether is my advice.

That car only has 6 gears, 4th gear is appropriate for accelerating onto the highway, you won’t be able to accelerate in 6th gear with that small engine.

Sounds like the car is behaving exactly like It should.
“ dealers can’t even put the correct oil into the car,”. How did you determine this?
“ rotate the tires correctly”. What do you mean by this?

@OmarGhoghawala It would be helpful if you said how you know the wrong oil was used and how the tire rotation was done wrong . Also if the transmission does shift into its highest gear at cruising speed than you may not have a problem . Are you comparing the performance to a previous vehicle ?