All of those can be issues. However, evaluate what you are blowing towards and what air you are using. I find that most students suffering this is a result of embouchure and air problems. It sounds like you are unaviodingly sub-toning everything in your low register. This is something that can develop overnight too. 1. Make sure your top and bottom teeth are in-line. 2. You can blow your head off down there, but if you are blowing warm/hot air....fuzz city. Keep it cold, focused & concentrated. 3. Make sure your top teeth aren't slipping around. Have a friend wiggle your saxophone neck while you play down there. Does the mouthpiece stay put? 4. Keep your chin relaxed. Look in the mirror. Is it bunched up, or looks like a strawberry (full of pits) when you play? If yes, your low register will be hard to control or respond.

I know this post is from 11 years ago, but for anyone (like me!) looking for answers to this problem, really, check your G# key. For almost half a year now, I've been trying different reeds and embouchures and wondering if I'm actually a terrible player. Turns out my key just had a tiny leak. I fixed this at home; didn't even need to take it to a repairman.