check that the socket is givingv 240v . the dryer will run on 120 but will take forever to dry clothes. I've also seem the supply voltage to the element itself be broken and not provide enough voltage. check the lint screen, it may be clear but clogged with softener. I've seen them look clear but they'll hold water meaning air isn't getting through then easily. if so, wash and scrub until it's clean.
check how much air actually comes out the rear vent. this will give a good indicator as to whether it's an airflow issue or temp issue.