I was just going over all the steps to make sure MDC decode was enabled. So, since you say the console is displaying the raw 4 digit data being sent by the radio, has the console ever successfully displayed an alias?
Just reviewing more steps... Are you saving the RDPS file, opening the Zetron dispatch software, reloading the configuration including entering the password if prompted? If you have more than one workstation not networked to a server you will have to reload the config on each machine manually.
Not saying you are doing anything wrong just trying to start from the beginning and work up to the finite details.