My vehicle is Mitsubishi mini pajero 2002 model ...

Thank you for contacting us 
Dear sir 
The problem with your car of the speed 80 km/h is that could be limited by the control module of your car, so you have to go to a specialist in pajero that will unlimit the speed by reprogramming the control module. 
And if he can't do that you may have to replace the control module. 
Best regards 
Eng. Mo'taz