New coolant part. Needle still dropped

I have a 2005 uplander. I have had the water pump,
thermostat, head gasket, temp sensor, radiator
replaced recently. Today as Im idling, my temp
guage moves slightly to the right. Then when I
pulled off it went back to half. This is the first time
its done this sense getting new part. What could be
wrong? Im a little anxious because of having so
many overheating problems in the past