Sorry if I'm being confusing. There are two separate things I cannot see how to do in 5.3 that I could in 5.2.
1) On the left-hand tab, where you create activities, I only see the ability to create a 'task' or various subprocesses. The 'Send Task' or 'mail task', for example, isn't listed anymore. (I do not see yet the method to create a call activity from an option when creating an embedded sub-process)
2) Also, The right-hand attributes tab is gone. I do not see a way to set the attributes on a task anymore.
I'm using a fresh install of 5.3 and a new diagram for this as well.