If you install the latest Google Analytics Add-On v2.1.1 from here https://www.gravityforms.com/my-account/downloads/ and install that from your Plugins page, you will have the merge tags for pagination to use on the Google Analytics Feed → Form Settings.
If you have any other questions, please let us know.
I’m guessing you have the soft validation feature enabled. If so, you will have to disable it for the pagination event to fire. The soft validation feature disables individual page submissions to create the most seamless user experience. Your form will continue to benefit from page transitions effect even if you disable it.