Loose rear end

[primal]

Ever since I had to change the rear tire on my bike, the rear tire hasn't felt the same. It would feel like the rear end would, for lack of a better term, slide around occasionally. It almost felt like I had an underinflated tire. At first I attributed this to it being a new tire, or the wind (it was pretty windy when I started riding again). But the past two days I've decided that its not my imagination anymore. After a bit of research, I concluded that it could be a few things:

* Chain too tight
* Loose spokes
* Rear wheel out of alignment

So, today I lowered the chain tension, tightened a few spokes, and aligned the wheel (difficult to do!). I also took the time to tighten the rear axle nut just a bit more. I went out for a ride and it seems to be riding much better, but I wanted to ask you all for your opinions on what else it might be. The first thing I checked was my tire pressure, and its fine, so I know its not that.

Any other suggestions? I want to make sure I haven't missed anything.