Les, I've had a couple of reasons for starter shoes not working. One is if the shoes were worn, which you've replaced so that's not it. I've had someone put the wrong springs on it so they didn't swing right. I've also seen where oil or something gets into the lip of the clutch where the shoes ride and cause them to slip. In that case you would clean the clutch and the shoes.
Make sure you have good movement of your clutch shoes and be sure they are clean and they should work. I've tried a little sandpaper on my surfaces occasionally as well.