Vantage 8.03.305b SQL: slow MRP

Has anyone experienced Vantage 803.305b SQL getting slower? Our MRP
used to take 16 minutes with 19,000 parts; now it takes 8 hours with
17,000. And it's not our data as uploading the same data into an
OpenEdge db results in MRP running in 5 minutes. We have a corporate
mandate to use SQL to take advantage of other software based on it.

We run Utility 5100, Recalculate Low Level Codes, after the upload. It
takes 7 hours.

We also execute Epicor's RebuildIndex SQL script. Then we run MRP.

Using multiple processes doesn't help as MRP hangs at different points.
It can finish using 1 process.

Any ideas?