Maytag dryer model MED5740TQ0. The dryer started not turning off a few weeks ago. Only about 3.5 years old. It will stay on in timed dry or auto dry mode. I have cleaned out the back, vent and cleaned off the sensor strips inside of drum. The timer still ticks but does not advance in either mode when drying or not drying clothes. Do I need a new timer?

You need to totally tear it down and clean all parts of it first. I would say you also need a timer, but while you are at the store you should get a belt and white lithium grease. Then tear it down and take out the air ducts and clean them well with soap and water. Clean all sensors and lubricate all bearings and support rollers. Then change out the timer and you will have a like new dryer.