Originally Posted by
MileHighMark
Don't grease your cables if you ride in sub-freezing temps. Instead, either run Teflon-coated cables, or use bare cables with a very thin, liquid lube (Boeshield or Pro-Link works well). I've found that my bikes with greased cables noticeably stiffen up when it's below freezing.
I would bet that this is your problem.
Try to "drizzle" a light oil (3n1, as an example) in the housing between your frame and RD for starters.