Page Editing Crashes when loading list of page parents.

I currently work with a website which has over 1000 pages and 4000 posts. The problem is, when adding new pages, or editing the existing ones, the page takes so long to load the whole list of pages in the database, that it has begun crashing. Well, actually it has started attempting to download the page (ie as a file) instead of just displaying it in the browser.

My question is, can the page parent dropdown on the page editing form be disabled or replaced? And are there any good plugins to do this?

Thanks a bunch,
James.