sports button on gear shift only alters change points for gearbox, keeps car in lower gear longer, but wouldn't affect top speed.
ready to be corrected.........
is that speedo 90 or gps 90, cos there is quite a difference, speedo reads quite high at around 85 gps, showing 90 /91 on speedo.
have you tried going in to manual select and putting it in 5th, then you can deffo be sure torque convertor is locked, and it's not hovering in 5th waiting to change down if needed.