What thermometer were you going by? I have found that the ones that come with the grill are always off. (mine's off 75º from my remote) Sound's like the one you were looking at was saying that it was hotter than what it actually was @ the grate level. The ribs should pull up the bone about 1/4" or more when cooked. For baby backs i usually cook them @ 230º using the 2-1.5-1 method. It hasn't failed yet.
I would get a remote thermometer if you haven't.
Alot of people use the Maverick ET-7 http://www.amazon.com/Maverick-Remot...5666004&sr=8-5
You should be able to find them cheaper online. From what I have read people here have not had a problem with these models.