2003 Ford Fiesta car less powerful

Hi,

I recently had a problem as my car engine was misfiring. I solved this issue through replacing the spark plugs and it no longer misfires.
However, since this, my car feels much less powerful. It doesnt misfire however when I am accelerating, the revs are increasing but the car moves forward less - if this makes sense? I am required to put much more revs on to reach the speed it usually reached.

I am unsire if this is connected but also since I fixed the misfiring, thr petrol is draining muh quicker.

Could you help with this?

Many thanks