1987 GMC Jimmy Temperature Problems

[14hatchie]

Hey gals and gals I need some help. My Jimmy temperature gauge keeps surging. Replaced new gauge and temperature control switch on the block, but temp. still surges. I replaced the thermostat twice and got the air pockets out. On both thermostats I replaced, the temp. would get 35 degrees above the rating then open up and drop to operating temp then immediately rise back up. What is causing this flucuation? Could it be the water pump is missing a vane or 2? Any help would be greatly appreciated.