VMware vSphere upgrades were described in Chapter 4, Upgrade a vSphere Deployment to 6.x, and most of the issues can be prevented by following the proper documentation, best practices, KB articles, and compatibility matrix.
Objective 7.3 for VCP65-DCV and VCP6-DCV are similar. It should be noted that the title has changed because there weren't big changes regarding the troubleshooting approach from vSphere 6.0 to vSphere 6.5.
The vSphere 6.5 Upgrade guide contains more information on this: https://docs.vmware.com/en/VMware-vSphere/6.5/vsphere-esxi-vcenter-server-652-upgrade-guide.pdf.