I just replaced my chain with a new one I bought from Xtracycle a few months ago. The one I replaced was probably my bike's original 10-year-old chain with the 30" extension provided when I purchased my FreeRadical in 2005. I decided to replace it because it'd become so gunked up and seemed beyond the value of spending time cleaning.
I've run into some strange troubles even though the new chain is exactly the same length. I found the new chain was actually too long and was dragging and sagging in certain gear combinations. I removed 3" and seem to have solved that issue. What remains, however, is some misalignment of my new rear derailleur (SRAM X-9), which I installed a couple months back when we had our last bout of mid-winter warmth.
What circumstances would cause me to have problems with the new chain that didn't exist on the old? I think the old other change I made was I loosened the body screw on the derailleur because Park Tool says SRAM derailleurs like their tension pulley to be about 6mm from the rear cog. Maybe I'll try tightening it again, which will add some tension to the chain. Do you think that will make the difference, too, for the derailleur currently skipping when shifted in sprockets 5–8?