I've encountered the same problem since upgrading my wife's iPhone 4S to iOS7. Strangely enough I haven't had any problems at all with my own gmail account on my iPhone 5 running iOS7. Have you already found a solution to this problem? Which type of phone are you using? 4s or 5? Maybe it's a device specific problem?
I got iPhone 4S - and still haven't found a solution to this problem :-(
I got 5. But I also face same problem.