What I do is with the truck cold first remove the rad. cap, then start the truck and let it run until you see the thermostat open on the temp gauge and the water level should drop, then retop the water off and reinstall the cap, it work's for me everytime. Also did you change the thermostat, because if you did and you used a cheapo like a stant or something then that can cause the temp to fluctuate like that, the cheap thermostats don't open at a consistant temp all the time. I use either Gates or AC Delco.
