Where should my Temp gauge ride with 180 stat

[steveo3318]

Ok so I bought the truck and the temp gauge would barely register cool. Found the truck had a 160 stat in it! Well I stuck a 180 in and now it reads barely above the first notch at times and on the notch most times. Kind of fluctuates, My temp shooter gun says its 180 to 185 all over the block. It has what looks to be a factory flex fan! I just ordered a new 53-811 sending unit but have the question of what sealant to use or none?

At 180 where should my gauge ride? And is it usual for these truck factory gauges to move pretty quick under normal stop and go driving conditions? "Like from a needles width above the first line to below it after a good take off and good radiator airflow?

thanks gents ahead of time.