Not sure what the specific detail are on your manifold, a pic would help.
I had a copper one for my first manifold with a bunch of (5/64? I think but not sure) size holes drilled in it. Never had one stuck sparge with this manifold.
Build a new manifold for a new cooler and cut slits. I used the finest cutting wheel on the dremel tool and cut a bunch of slits. I thought I'd maybe get a finer filtration and maybe cleaner wort doing this. After three stuck batches I drilled holes (using the same bit I used for my first manifold) between the slits that I had previously cut. She runs like a champ now. Full speed and no stuck sparges. Wort is clear too.
So I would consider maybe using a slightly wider cutting wheel or just adding more drainage points to your current manifold. The added holes did it for me.