low fuel efficiency and gear shift at higher rpm

i own a automatic L&K laura (octavia 2).there was a problem with a cam shaft.therefore i got it replaced along with the eight cups.i also got the car serviced.

now car works fine but with lower fuel efficiency.earlier it used to give 24 26 kmpl at 70 km/h when in 6th gear.now it just gives 17 or 18 at max.also the car take 2 and 4 gear too long.many times they go across 3000 rpm to change.i told my frnd.he say it can be the injection of fuel is simply increased by mechanic.so the fuel efficiency is low and and takes more rpm to change.

i will visit the mechanic bt first wish to know your all opinion about this.

thnk you all