# the fix:
@items = grep {
    my $keep = !exists $del{$_};
    $i++;
    $index -= ($i < $index) unless $keep;
    $keep
  } @items;

# the results
Benchmark: timing 100000 iterations of BrowserUk, dpuu...
 BrowserUk: 13 wallclock secs (13.72 usr +  0.00 sys = 13.72 CPU) @ 7288.63/s (n=100000)
      dpuu: 10 wallclock secs ( 9.88 usr +  0.00 sys =  9.88 CPU) @ 10117.36/s (n=100000)
             Rate BrowserUk      dpuu
dpuu      10117/s       39%        --
BrowserUk  7289/s        --      -28%

##</code><code>##

Benchmark: timing 100000 iterations of BrowserUk, dpuu...
 BrowserUk: 10 wallclock secs ( 9.26 usr +  0.00 sys =  9.26 CPU) @ 10795.64/s (n=100000)
      dpuu: 10 wallclock secs ( 9.87 usr +  0.01 sys =  9.88 CPU) @ 10118.39/s (n=100000)
             Rate      dpuu BrowserUk
dpuu      10118/s        --       -6%
BrowserUk 10796/s        7%        --

##</code><code>##

@items = grep { ++$i && !exists $del{$_} || ($index -= $i-1 <= $index) && 0 } @items;