I would install a high quality mechanical temp gauge and compare it to the electric gauge. You may just have a readout problem. You could also have a marginal cooling system. I have a large fluiddyne radiator and dual fans. It doesn't do what you are describing. The fans only come on when I am below about 35mph in traffic unless I am in high summer temperatures. On the highway, they are rarely on.
P.S. I have two readouts. The second is on my FITech display that has its own sender. The stock gauge doesn't track very well and I consider it a crude indicator.