How do I use tmutil to figure out what's wrong with my Time Machine?
You can use timedog to see what's being backed up each time. 

Usage:


Open Terminal (in /Applications/Utilities)
cd /Volumes/Time\ Machine/Backups.backupdb/[Computer Name]
Note Time Machine may be different on your system.
Replace [Computer Name] with the name of your computer (see System Preferences => Sharing).
/path/to/timedog -d 5 -l
For instance, if you unzipped timedog to your Desktop, the path would be ~/Desktop/timedog


And then look at the output