I solved a lot of my FC's and inability to install some SC Roms by backing up my SD card to my computer and reformatting it, then I went back to stock, then I installed the SC Rom, then I copied back what I needed. I had a lot of folders that had accumulated over time that I didn't need anymore. It solved my problem after trying many many tips that others were posting here.
I also had battery life issues and got rid of all widgets and added them back in one at a time. I found that MLB At Bat 11 was the worst battery hog, it would drain my battery in an hour. Now I can go all day without charging while still using GPS, Wifi, browsing, email, messaging, twitter, facebook, calls. Video (Video player or Slingbox) still sucks down the battery but that is to be expected. I am currently only using the google news, and weather channel widget.
I also highly recommend the ES File Explorer app. It is so nice to be able to copy over a file without connecting to the computer via usb.
SC 2.9.1 is the best ROM I have used so far and it is working great.