Apple Mail Search is acting strange

Hello.

I have been having some major issue with Apple Mail (6.5) in its search function.

I have been a heavy user of Apple Mail (over 15,000 emails on the program- and archived every year) for many years, and never had this issue.

When I search for a key word it does not find it! I noticed that this not to work on emails in my In Box or Sent Boxes (Gmail email POP). If I move a specific email to a newly created folder On My Mac and then search, the keyword will be found in the email in that new folder- but never on the orignal Inbox or Sent Box! Also, the search works fine for senders of emails (by name) if I search for them.

The issue is mainly in finding a key word in the content of an email and particurly in the In and Sent boxes!

I tried EVERYTHING I could find online from reindenxing the whole Macintosh HD, deleting Envelope Files... I even deleted Apple Mail and then reinstalled it from Mountain Lion DVD! STILL same issue.

To test things, I exported Mailboxes to another Macbook Air I have (brand new) and then imported these mailboxes into the correct location (Inbox, Sent...etc), and the search there worked fine!

ANY IDEAS, as this is frustrating and I am seriously considering switching to new email client after all these years.

Thanks,