Suzuki GSX-S 125 after chain set change Slower

Hello, I was about 1 week ago at the 8.000 check for my Suzuki GSXS 125 it was so far all ok until also my chain set which was probably down so a new one had to come here I always managed on the straight according to Tacho 120kmh but now I manage with all the last need the 105kmh why is that so? Did something go wrong?