I had a similar problem with my oven (electric). One thing to check out is if it is holding the desired temperature. Get a small oven thermometer and place it in the oven while you are baking something. Try to check it without opening the door, but what you want to find out is how cool does the oven get before the oven comes back on. You might also check the burner and make sure the holes in the gas jets are not stopped up.