my @rows;
while (@products) {
    push @rows,
    {
     'loop_products' => [splice @products, 0, 3],
    };
}
$template_body->param(
   loop_row => \@rows,
   );

##</code><code>##

<TMPL_LOOP NAME=loop_row>
   <TMPL_LOOP NAME=loop_products>
       Display one product here.
   </TMPL_LOOP>
</TMPL_LOOP>