My GE Profile Range has suddenly started baking food only around the outside edges, and only lightly heating it in the middle. The service people eliminated the wire harness at the temperature sensor of the oven. When that didn't work, they replaced the oven control. I cooked a frozen lasagna and the other than the outside edges. the inner two-thirds were barely warm. Now I've been told I use the wrong type of cookie sheet to put the lasagna on, that I should use the convection, etc. etc. My oven has worked all along. This is a brand new problem. What do I do now?