Are the bearings OK? Sometimes there's simply one ball bearing under the central shaft of the extractor - and it is easily lost as I know to my peril. And if the top bearing is binding, the thing could slow down. A drop of olive oil might do the trick.
If the rotating frame is dragging on un-discharged honey in the base of the extractor, then the motor will struggle.
May your bees read the same books as you do.