If screw is bent enough to cause stalling then you should see it easy enough.? Bent screw will cause a vibration first then if really bad will cause stalling.
It it is indeed a Lead screw and not ballscrew(Hard to tell from pic) I would look at the lead nut it's self to see if it's tight or badly worn and it's binding under load.! What material is the lead nut made from.? looking at the colour of the lead screw I suspect Delrin.? Can you post a picture of it.

If replacing the screw/nut then really you want a ballscrew. They are far superior to lead screws and if bought from China then will probably cost only slightly more than a decent lead screw bought in this country. They will also machine the ends to your spec if the ends are custom machined, which I suspect they will be on this machine.!