To disable at over 2000, you can use in the file:
/includes/modules/shipping/table.php

the code in RED:
Code:
    // disable only when entire cart is free shipping
    if (zen_get_shipping_enabled($this->code)) {
      $this->enabled = ((MODULE_SHIPPING_TABLE_STATUS == 'True') ? true : false);
    }

if (!IS_ADMIN_FLAG && $_SESSION['cart']->weight > 2000) {
  $this->enabled = false;
}
    if ($this->enabled) {