Slow lift can only be down to two problems. Either the mechanism is stiff and putting too much load on the motor or the motor itself is unable to drive the mech. You could try being liberal with WD40 around the mechanism and see if that improves it. Be warned however that you should strip, clean and regrease it properly afterwards.
As for the motor, reseat the plugs and relay, clean the earths, reseat the fuse and hope!