It's possible that the computer you are hooking it up to is not powerful enough to capture 1080p 30fps? If it is Windows you could pop your Task Manager open to see if any system resources are tapped out (near 100%).
You could also try lowering the resolution ..all the way down (just as a test) to see if you get the synch you want. Then just keep upping the resolution until you get a good blend that works.
Windows 10 has a built in camera app you can use for this test. =)