check engine light, car running fine, code coming up coolant

I recently bought a 2004 Chevy Impala that had a blown head gasket so the engine was replaced.  It ran fine on my two hour drive home right up until I pulled into my drive then the traction control light came on then shut right back off.  There did not appear to be a reason for it.  When I turned the car back on it was off and didn't happen again for a day or so.  Then a couple of days ago the traction control light came back on and then the warning light came on along with the ABS light.  When I stopped and turned the car off and then later on again they were back off and stayed off for a few days.  But then my check engine light came on around the same time I replaced the gas cap.  I switched back to the old gas cap to see if that made a difference which it didn't seem to.  I looked more closely and noticed that there was a thick layer of dust around the opening which the cap seals to.  I cleaned that off carefully and replaced the cap.  Then went to auto zone a couple of days later and they said that it was reading as low coolant.  It appeared that the coolant was fine but added a touch more to be sure since the fill line was near the level of the coolant.  Light was still on.  I researched bad thermostat and coolant temperature sensor.  I am not seeming to overheat (I have been paying close attention to any signs) and the temp gauge inside the vehicle reads fine.  The car is driven about 20-30 miles on the interstate in the mornings and afternoons with a bit of city driving in the afternoons when we run errands.  We are getting about 26-28 mpg.  We bought the car last Sunday so not a long history with it.  Oh and I have noticed a couple of times that when I try to accelerate that the car will accelerate then seem to have a quick pause then continue to accelerate.  That may just be me, though.  It has only happened twice.  Any ideas?  I figured I would replace the temperature sensor and thermostat since those should be easy to do myself.