Temp guage not reading correct??

Have 72 340 in my car and the temp guage is reading just above low temp and below running range ..but with temp gun motor is running 180 ish and steady no bubbling or issues expept guage ..can it just be messed up and need replacing??.. car was sitting for almost 20 yrs..flushed motor ..new water pump..new alluminum radiator..new intake manifold gasket and hoses..new temp sensor.new heatercore..to tell you what I've done to the cooling system so far..