Working through a sorted nodeset 3 at a time

Hi,
 
I have some XSLT that looks like :

   <xsl:apply-templates select="DATA/ROWS/ROW" mode="sorted_list">
      <xsl:sort select="FIELD[(_at_)ID='1']/VALUE" order="ascending" />
    </xsl:apply-templates>

    <xsl:template match="ROW" mode="sorted_list">
        <xsl:apply-templates select="current()[position() mode 3 = 1" 
mode="hits_page" />
    </xsl:template>

    <xsl:template match="ROW" mode="hits_page">
        hits_page : <xsl:value-of select="." />
    </xsl:template>

I don't get anything output by the hits_page template.  I don't think using
'current()' is 
correct here, I've tried ".[position() ......]" (and a few others) but this
gives me 'invalid 
XPath expression'.

Hopefully there's just a bit of syntax I don't know about.

Thanks

Steve