Sorry if this has already been discussed to death (I missed a couple of days of posts to this group)...
When I did my 10", Jerry Wilkinson (made many of Galaxy optics' mirrors, and has also worked in several optical shops) had me scratch the pitch lap using a stiff wire brush (the kind sold in hardware stores for removing paint) - buy a brand new one, the sharper the ends of the wire bristles the better (you want lots of very sharp edged scratches). He had me scratch the lap quite frequently (every couple of wets, you can feel the lap start to grab more as the scratches press out and round off).
The scratches really sped up polishing and reduced the grabbing tendencies of the lap.
Bob