Help a newbie out! I have a new Gary Fisher Nirvana which works geat except for the chain is skipping in low gear (small front chain ring, largest rear gear). I am fairly new to cycling and we have some pretty steep hills where I ride (Mammoth Cave National Park area), so from time to time I have to use the lowest gear on some of the hills. The rear derailleur is a shimano deor. I have taken it to the LBS and they adjusted it, but it seems worse now. Is this a chain problem or a derailleur problem? Any advice would be appreciated.