Oven doesn't maintain temp

I purchased my oven about a year and a half ago and I’m currently having a problem that I think may have to do with the clock or part #AP4099018, but I’m not 100% sure. If I set my oven at 350 it might heat up to the temp and it might not, it’s inconsistent. If I use a temp of 400-450 the bake light begins flashing after about 10 mins. If I shut the off oven off and turn it back on the temp may only be in the lower 300’s. Or I may be able to use it at 350, but after about 10-15 mins it starts to lose temp. I’m not sure if the above listed part would fix my problem. What do you think?

Thanks for your help in advance.