My oven isn't holding the heating temperature I set. For example, if I set the oven to 350 degrees, it only heats to 250.

If I increase the temperature it sometimes warms more, and sometimes stays the same 250 degrees. I'm using an oven thermometer to check temperature.

Last November I replaced a blown thermostat and lower heating element. The oven worked fine between then and now.

When I turn the oven on both the lower and upper elements turn on. The lower element glows red, but the upper does not. When I turned it to broil, however, the upper element did turn red, and the lower element did turn off, so I "think" the elements are working properly.

The only thing I can think of at the moment is that maybe I have a faulty thermostat, or maybe a loose or poor connection in the wiring. Does this make sense? Are there other things I should check for?