yep, i have been having the same problem...
i tried every possible thing i could think of.
Me and my mate (he at his home) tried to play we couldnt even finish off the first 9 holes!
We both made sure to put our routers in DMZ mode and forward to XBOX360's IP address, just to make sure it is not something on our end.
It is just unbelievable. PGR3 plays flawlessly while this is just shambles. We tried about 15 different matches last night, every time at some point it just disconnected and threw up an error message.
I was looking forward to being able to play him on xbox live, now i deem this game worthless as i do not play single player.
They also cut out a lot from the game, seems like a slimmed down version in comparison to earlier tigers i played. No mini games, a few courses...