If you have to disable IPv6 to get Google Play downloads to function, then it sounds like there might be an issue with the IPv6 settings on your WAN or LAN interfaces, or your ISP is having issues.
Some ISP's in the US are still in the process of deploying IPv6 (and there are some that still haven't even started rolling it out). You might get an address, but it may not be a stable connection as they continue to roll it out throughout an area. Or if you have an ISP that isn't supporting it, you might need to disable it on your LAN interface to make sure that the router isn't advertising itself as an IPv6 router.