With the 10 Speed Auto, 6th gear is direct drive with 7, 8, 9, and 10 all being overdrives. Depending on the load on your car (car full of people, AC blasting, etc), going 90 MPH might have the car drop into a lower overdrive gear (which is so weird to think, my first two cars only had 4-speed autos, now I have a car with 4 overdrive gears).
And @alorentzen is right, Sport mode will keep the car in the first 8 gears only. You can manually shift up to 9 and 10, but if left to auto mode (you can just pull and hold the upshift paddle for a couple seconds and the computer will go back into Sport Auto mode) it'll keep you in the lower gears for responsiveness.
I've posted about it before, but the one thing I thought was interesting is that you can't get the car to go into 1st gear. Try putting the car in Sport and paddle shift down when coming to a stop. No matter how slow you're going, you can't get the car to engage 1st gear. But when taking off from a stop, it'll start in 1st gear. Someone mentioned here (or reddit...?) that 1st gear is probably a "launch gear" and the computer prevents the driver from shifting into it.
And @alorentzen is right, Sport mode will keep the car in the first 8 gears only. You can manually shift up to 9 and 10, but if left to auto mode (you can just pull and hold the upshift paddle for a couple seconds and the computer will go back into Sport Auto mode) it'll keep you in the lower gears for responsiveness.
I've posted about it before, but the one thing I thought was interesting is that you can't get the car to go into 1st gear. Try putting the car in Sport and paddle shift down when coming to a stop. No matter how slow you're going, you can't get the car to engage 1st gear. But when taking off from a stop, it'll start in 1st gear. Someone mentioned here (or reddit...?) that 1st gear is probably a "launch gear" and the computer prevents the driver from shifting into it.
