how to be the last hook_page_alter called?
To make your hook last called you can make use of hook_module_implements_alter
like the following:

function MODULENAME_module_implements_alter(&amp;$implementations, $hook) {
  if ($hook == 'page_alter') {
    // Move MODULENAME_page_alter() to the end of the list. module_implements()
    $group = $implementations['MODULENAME'];
    unset($implementations['MODULENAME']);
    $implementations['MODULENAME'] = $group;
  }
}