I don't know Gmail-Loader even works at all any more... as far as I
know it hasn't updated in years and there has been huge changes to
Gmail since then.
If you're willing to use a desktop client for just the time it takes
to upload you can get the problem solved and save all of the original
info (including time stamps). To do it:
1. Enable IMAP on Google
2. Configure the desktop client to access Gmail.
3. Import the MBX files into the client
4. Drag the emails over to wherever you want in the Gmail folder listing.
5. Wait
6. And wait.
7. Disable IMAP and use the web interface!
Ryan