So the clutch is new, huh? Hmmm...
Was the face of the pressure plate cleaned before it was fitted? It's been a while since I was on the tools, but from memory the pressure plate face is greased by the manufacturer to prevent corrosion. If it wasn't cleaned, it would have contaminated the clutch plate. You can try getting the contaminants out by dousing it with methylated spirits and setting it alight (the heat shiuld draw the contaminates out), but it's not guaranteed to get it all out and should be done under VERY controlled circumstances!

Also, was the flywheel machined beforehand? What about the rear main oil seal? Unless the seal was replaced (or is sealing well), you might as well replace it while you're there.

Good luck today and remember to keep the prop shaft in the back of the 'box!