Thanks for the reply. I've gone through all the policies and have tried to get it to update, but I'm not sure what's wrong. I looked up the Extract SSL Certificate (x64) policy, and decided it needed to be enabled (my ITMS server was the only target). This then brought my server into the Deployment Package Server Components policy, and I've gotten that installed. This installed a different agent, though - it's Deployment Package Server Components. I don't know which policy even controls Package Server as listed in the screenshot above. Do you know which policy controls this? I would've presumed that the Deployment Package Server Components policy would take care of it.
.net 4.5.1 is installed (this was done prior to upgrade).
**EDIT: FOUND THE PROBLEM POLICY! It wasn't with the other agents (Symantec, please make this easier to find!). Go to Settings > Notification Server > Site Server Settings, then Settings, Package Service > Advanced > Windows in the left pane and enable the Windows Package Server Agent Upgrade. To expedite its push, I did a inventory & config update request for the server, and the package went right out.
See location of policy below.