Alfine 8 slipping

Are you sure teh shifter is compatible? I thought Alfine 8 had to have its own propriatry shifter or am I talking crap?

I've found with setting up Alfine 8's in the past they are not that sensitive to being either side of the mark a little (+/- about half the width of the mark), HOWEVER, the mark is often not painted on in the right place!
Seen this on 2 hubs where the mark was a good 2-2.5mm away from where the 'ideal' shift point was.
Lastly, remove the cable from the hub end and thoroughly check the cable to make sure its smooth and not snagging as this could be causing your issue.

This is how it is with mine. If I adjust per instructions then I get slippage. If I have slightly more cable tension so that the yellow lines don't line up then it is fine.