I ran 2 xboxes last night with GF OFF and only using reserved IPs for the boxes, NAT Endpoint and uPnP enabled. No other devices were online. NAT was OPEN on both and had a good time playing. 4 green bars mostly.
Going to test wtih GF ON and uPnP OFF next.
@Drunkjug, if you turn on the box with moderate NAT first, does the 2nd box then report moderate NAT?
Have you reset the network settings on all boxes? Try swapping the IP addresses on the router to see if the problem travels or persists.
Run a couple of tests like I'm doing:
Just disable GameFuel and leave uPnP enabled, and NAT set to endpoint independent and use the reserved IPs.
Then try: Enabling GameFuel and disable uPnP
When you make the changes for testing, make sure you turn OFF the boxes while making changes.
Let us know what you see.