trac off light and rough shifting

I have a 2000 2.4L alero and after about 15min of driving the trac off light comes on the car shifts gears really rough. I restart the car and the problem will go away for a couple of minutes. This problem has been happening for a long time, but very intermittently, would happen a bunch of times, then not happen for a few months. Now it happens all the time. I don't think it's a hub problem because the ABS light doesn't come on. Could this be a crankshaft position sensor? If it is, is it easy to change out?

I have the same problem!!(99 alero 2.4)! im brigin it to the machanics next week and i'll tell u what i found out. it usually shift hard from 1 to 2..had the transmission fluid clean...it helped but a month later the hard shifting is back!!!!