Can't edit form fields and very slow performance

Hi everyone,

I am facing some problems with gravity forms, which worked perfectly for almost a year. When I choose the form overview and all my forms are being displayed (about 20) the performance is so slow that each form in the list takes some seconds to display. When I click on one form to edit it, it will take about 30 sec to one minute to display the fields. But in the end, I can't edit the fields. It seems like a css / jquery problem to me. Server performance is not an issue, as everything else performs well.

Details: Wordpress 3.5.1
Gravity Forms: 1.7.1 (problem exists since 1.6.1, update didn't help)
Other Plugins: WPML (2.8.1), Gravity forms multilingual (0.9.3), WPML string translation (1.7)

I've deactivated a couple of other plugins with no success. Is there a chance that uninstalling gravity forms (exporting forms first) and reinstalling will help?

Thanks in advance,

Tim