I have an old Maytag gas dryer model DG9800. It takes 1.5 hours to dry a regular load, with some parts of clothes still being a little damp. The inside temperature is just warm (95-100 F) after 20 minutes of running, and the temperature reaches 120F after 1 hour. Based on my observations, the flame went off too soon, before the temperature reached the target. I checked the vent from outside and the air seemingly went out fine. I have installed a new cycling thermostat, new solenoid coils, and a new hi-limit thermostat, but it makes no difference. What else could be wrong? Thanks.