I am having the same problem. It lags a lot, although sometimes it works just fine. I loaded Gsam battery monitor and sometimes it lags in notifying me of the battery level and will suddenly show a huge drop. I think there are some kernel wakelocks that prevent the phone from sleeping and use excessive battery, but I don't know which ones are normal, so I don't want to try to disable anything. I did a cache partition wipe but no difference. I was wondering about formatting the cache partition.
Sometimes when my phone is really struggling, and won't respond to touching the screen, or the keys at the bottom, the back light for the keys will blink slowly. I'm not sure if blink is the right way to describe it, but basically the back light turns off and back on for a few moments at a time. I have checked to see which apps are running, if possible, and the ram is around 90% in use, and will fluctuate a little, showing different apps running and then disappearing from the list. I was wondering if anyone else has seen this happen or knows what is going on.