Well a couple of suggestions. In your account settings Menu->Tools->Accounts,
Edit you gmail account. On the account tab change retrieve to headers only, and retrieval limit to last 50.

You will probably have to nuke the account and redefine it, because you already have more than it can handle. You might also try going into gmail on the web and archiving your inbox. This will move many of your old emails from the inbox to the "All Mail" folder.

Bruce