Actually after replacing the timer and the thermostat, I discovered the problem was actually the dryer vent. I had two 90 degree elbows in the vent to save space behind the wall, but that restricted the airflow through the vent and did not allow the thermostat to work properly. So I took out the elbows and ran a single flexible vent with rounded curves. It took a little more space, but the airflow improved and now the thermostat works fine. Consider cleaning your vent and/or straightening as much as possible to allow for the easiest and maximum airflow.