I'm looking for assistance and hope you guys/gals can come through for me.

I've got a 2002 Sentra GXE with 76K miles on it. Three weeks I got an SES light on the dash and the car started overheating. I went ahead and had the thermostat replaced at a local shop. At the same time I also had the plugs and fluids replaced.

Now for the last two weeks I've had intermittent heat but the car will occasionally run very hot, but not over heat. I'm not loosing any coolant which leads me to rule out a gasket leak. The only other symptoms I'm seeing are a slight shudder on cold start which resolves itself very quickly and the perception of a stiffer gas pedal on acceleration from a stop. I'm not sure if those are directly related or not.

I'm struggling with what would be causing the intermittent heat and running hot. I'm willing to replace the thermostat again, but I'm not sure if I should be looking elsewhere.

So, fire away! Thanks in advance for any and all assistance.

so the blower sends air into the cabin its just cold air or it doesnt send anything at all?

That's correct. Most of the time it's barely warmer than outside air temperature. But then it has days like today where it works fine. Meaning, the heat blows very and the engine doesn't run hot. Other times, it will run hot and suddenly start blowing heat and the engine will cool off.

have your coolant flushed, not drained, but flushed under pressure