Check your email settings on the X and make sure you have the "data push" enabled (checked) and a short interval for "fetch" such as every hour. If push isn't possible, the fetch schedule will kick in. Also make sure you don't have "sync only over wi-fi only" enabled, unless that's what you want.
gmail>settings>email delivery>data push/fetch schedule/sync over wi-fi only
Also, check in the regular settings to be sure the sync gmail is enabled...
settings>accounts>gmail>sync gmail (check)
I have my gmail account set up to collect email from my 2 pop3 email accounts and deliver it all to my X on a push basis. Works fine. Also, when this is done, if you delete either on your desktop gmail or X, the email is deleted on both (need to remember this when deleting from the X).
Also, gmail doesn't push the spam, which keeps your X from getting inundated with junk email. I love that!