Attaching a load to a Uhing traverse drive
Using a larger drive does not help. If a load is being attached improperly then the Uhing drive will lose thrust and will slip whether you use a small Uhing drive or a large one.
One size does NOT fit all
Unless the application is identical -- and I mean identical -- in all aspects, a Uhing traverse drive that is your dream machine for one application, can be your biggest, worst nightmare in another application for which it was not designed.
It’s a friction drive
That means that the bearings put a significant "bite" on the shaft. Anything you do in your set up to interfere with that "bite" will cause problems for you.