Temp Needle Overactive?

[lexus082]

I recently changed my coolant reserve tank and refilled the new one. My temp needle used to always stay a "needle width" above the line a little bit below the center of the gauge. After changing the reserve tank the needle now slowly rises up to that point at which it used to be normal. But I guess depending on the rpm's it drops quite a bit and then will rise back up. Or will I am on the highway it may constantly go up and down just maybe a quarter of an inch in motion. The heater doesn't seem to be as consistent as it used to be either. Is it possible that there is air in the system and I just have to have the coolant flushed?

[SKperformance]

You may have air which is highly likly .