G.E. Electric oven not staying hot?

When you cut it on initially the bake element and the broil both cut on for pre-heat. one broil cuts off when the pre-heat is done, the bake element doesn't stay at the right temp. If i put it at 350, it doesnt stay at 350 and i have to keep increasing the temp to cook my food. biscuits took almost an hour and the temp had been raised to almost 500