I've been playing MC for a couple of years on this computer with no problems. A short while ago (before 1.7.4 upgrade) I started to see intermittent lag when moving. It got worse and now MC is unplayable. Note: EVERYTHING lags. That includes movement, command keys (ESC), and setting MC options. For example, I just went into Video Options, clicked on Mipmap Levels, and it took 5 seconds for the slider to move. It also now takes MC several seconds to exit, whereas before it was almost instant.

The rest of my apps are running normally. I have done a full virus scan. I completely deleted MC, then reinstalled it and tried to run a vanilla version (local, single player) with no other apps running, and the problem persists. I am totally out of ideas.