interesting.. I've used zipship for as long as I've used zencart and never had to do this.

However I do have this coding amendment in mine -

//$this->dest_zipcode = substr(strtoupper($order->delivery['postcode']), 0, (int)ENTRY_POSTCODE_MIN_LENGTH);
$this->dest_zipcode = strtoupper ($order->delivery['postcode']);

Dumb dumb me didn't comment why, but I wonder if it might be a simpler solution...