Flucuating temp guage problem

Hello, I have this ongoing problem and I dont know what to do and im sick of it already. The cooling system is flucuating and if I let the car sit and idle the fan comes on normally. If I take it for like a 20 minute drive then get to a light or a drive thru the temperature guage rises until a certain temp. (I brang it to a shop and they said it was the fan switch so I changed it and I still have the same problem. They also said the fan isnt coming on till 260. I also have a 1-3 minute video of me parked and what the guage does and where in the guage the fan turns on. What else could it be?