Task Escalation Alert

If you feel that you need more control over your messaging than is offered by an Escalation, then instead of an Escalation, configure an Exception on your task that flows into  a Send E-mail node.
 

This will, of course, kill the original Task (and then replace with a new one) which may not be the outcome you want. So if you want the Task to still be Active, but want (as Robert proposes) to send a fully configurable email you can use the 'Send Message Event' option in your escalation, and add a Receive Message "listener" in the same process model:

This will, of course, kill the original Task (and then replace with a new one) which may not be the outcome you want. So if you want the Task to still be Active, but want (as Robert proposes) to send a fully configurable email you can use the 'Send Message Event' option in your escalation, and add a Receive Message "listener" in the same process model: