Cruise control at Higher speeds always +/- 5

May be this is a hardware defect in my car. I need to confirm
My speed controls + and - work fine in lower speeds, and increment / decrement by +/- 1

But at higher speeds , say above 60 , I am unable to do +/- 1. It always does +/- 5.
Only one in 10 times, it does it by +/- 1 above the speed of 60.
My fingers are fine. I have tried doing it very fast , as the manual says , but unable to achieve +/- 1.
I was thinking of asking the dealer to replace the buttons, as the manual says , doing it little should make it +/- 1.

One click up or down gives a +/- 1 change. Pushing the button fully up or down gives a =/- 5 change.

The switch is a 2-stage thing...it sounds like you are pushing it into the second stage, which, in the USA anyways, causes a 5mph bump verses 1mph. There's a little resistance between the neutral/center position and getting the 5mph bump. If not, you may have a defective switch.