Kenmore Model # 790.9642240C. Oven takes 30 minutes or more to warm-up. Not new problem, has done this since purchase several years ago.

I quess "several years ago" would have been the time to address this situation when it was under warranty. If this is an electric oven, you could have a burned out element. Turn on the oven, set to 400 and see if both elements are glowing red. If not, you probably need a new element. If a gas oven, there could be some dirt in the orifice. I would also have someone check the wiring at the stove connection to make sure you are getting 240VAC if electric.