Aaron,
You can't actually call a specific page from a postscript attachment using the execpage() command. That command is used to execute form pages from the current form.
When you execute a postscript attachment, the entire attachment is executed--not just specific pages.
The two workarounds I see for your issue are:
1-Do a copy/paste of your pages from one form to the other.
or
2-Have your postscript attachments contain only the required pages. That way, when you execute the attachment, you have the desired result since all the pages of the postscript document are being executed.