I live in E.Ga, but grew up in E.AL. I does get cold !! 20degrees w/70% humidity and 20mph wind is plenty cold.
It is probably a combination of things.... I too have an SKS and shoot that load. I actually prefer either 2400 or IMR (H)4227. They work the action a little more briskly too. For best cold weather function, be sure to clean well and remove all remnants of bullet lube from action after shooting. This may have "gummed" up the works a little too. I've been meaning to try some H4895 with the 155's, but have put it off because the IMR3031 I tried really threw the brass into right field !!! These two powders may be the solution youre looking for.