Significant drop in performance on the mountain (3% incline)

Hello together, I bought a new scooter above all and drove a long distance of 60km today in sunny weather.(Landstraße,Slopes and Climbs) My first overall impression was very positive, however, it is to be criticised that the scooter on the mountain loses over half of the speed.Just=approx.63 km/h on the mountain of steady waste up to 23 km/h no matter which slope. What can this have for reasons? Because I did not need to buy a 2stroker and submit my 4stroker. Thank you