Whirlpool Oven Problems Pre-Heating

so, my wife and I recently discovered that when our oven beeps and tells us that it’s at 350 degrees (for example), it’s lying to us. After getting an oven thermometer and checking it once the oven beeped, we realized that it’s only at about 250 degrees. If we leave the oven for another 15 or 20 minutes, it will get up to temp, and stay there.

I called a local appliance repair guy and he came and checked the oven out with his meter and said everything looked OK to him. After ranting for 10 minutes about the stupid design of a hidden bottom element, he asked if my wife’s cakes and pies and etc. were cooking OK (which we had a good laugh about later since we cook fries and pizzas, for the most part). I told him Yes. However, I think I may have given him some false info. I’ve since noticed that things are cooking unevenly, and faster on the bottom.

Does this sound like an element problem, or perhaps a problem with the communication between the internal board and temperature sensor?

Thanks.