Check that the cable is in the lever correctly, no rubbing etc.
Also make sure that the noodle has the inner pipe inside, and that it is conencted properly.
And that the pads are not catching on there return on the tyre.
That the cable isn't fraid inside the outer, easily done.
Make sure that the lever pull is adjusted all the way towards the front.
No sharp kinks in the cable, inner and outer.
Incorrectly adjusted spings? doubt that would make it slow though.
Really all I can think of mate, try all those and It should be good (Y)