UpdatePanel refresh problem using __doPostback

Hi,
   I've a page with UpdatePanel that hosts a web part manager along with two web part zones. User controls containing GridView, panels, etc. are used as web part. The UpdateMode is conditional. I also have an UpdateProgress indicator that shows when update takes more than 500 ms. I'm using PageMethods to check for updates to the page(instead of ASP.NET AJAX timer because it postbacks the whole page). If page needs to be updated, then I call __doPostback for the UpdatePanel. In the UpdatePanel load on server side, I then rebind the data. It works fine. But often posting back this way takes a LONG time, UpdateProgress shows the spinning gif and I get timeout error in PageEndrequest. I increased the AsyncPostbackTimeout as was suggested in some posts, but it didn't help.  As a workaround, when I get timeout, I reload the location in the browser but it is not a good user experience. Has anybody come across th ...