Shuddering gears in brand new FG Falcon

Less than half an hour after picking up our new FG Falcon G6 we felt it wasn't changing gears well; there was a shudder between gears. After checking it at 700 km the dealer acknowledged that there was a shudder and took it in to check it. When we got it back we were told they couldn't find the problem and that they drove two others and they did the same, so that's the way it is. We have since found other owners who are have also had the same problem. We have also heard through someone working at Ford that Ford knows of the problem and is working on it. So we took it a bit further and went for a test drive in a XR6 at another dealer and guess what, at 1500 revs the shudder comes in! When we took it back and told the salesman he told us it was a faulty car but we would get a good one. He also invited us to drive his new XR6, which he said was a good one, but he was alarmed to find that his also had the problem. We don't know where to go next and why didn't the dealership tell us of the problem when we were buying to give us the option of changing our mind, I don't think they should be selling if it has problem before you even pick it up.