How do you get iPhone to share contacts with Mac Messages app? When I get a new text, it appears both in the Messages app on my iPhone and in the Messages app on my Mac. The iPhone text show the person's name, and the Mac text only shows the person's number. I have Contacts checked under iCloud sync. Both OSes are latest.
I have been having this same problem and as I go through this thread I found that I could answer yes to everything, but the problem persisted. 

I ended up opening the Contacts page on my Mac and while the contacts I needed were in "All Contacts" they were not in the "On My Mac" so I highlighted them all under "All Contacts" and did a drag and drop into "On My Mac" it fixed almost all my problems. 

The ones that it didn't fix I found out that the formatting on the phone number themselves were not correct. For example the one on Mac messenger was 1(234)567-8900 while the contact card did not have a 1... so, (234)567-8900. Changing those two things fixed everything.