My Issue Solved!
I was able to isolate the file (
com.seagate.SeagateStorageGauge.plist) in the following location
Go Menu > Computer >Macintosh HD > Library > LaunchAgents folder. I removed the file and my machine sleeps instantly now. The offending file was installed along with software to manage my Seagate GoFlex USB 3.0 external drive. I shouldn't need it.
You can try to reset the SMC (that didn't help me), but it is unlikely this would be the issue in a brand new machine. Otherwise, the issue is most likely in one of the following locations:
- System Preferences > Users & Groups > Login Items
- Go Menu> hold Option > Library > LaunchAgents folder
- Go Menu > Macintosh HD > Library > LaunchAgents; LaunchDaemons: StartupItems folders
Go through these locations, removing items or temporarily renaming the folders one at a time, restarting and testing sleep after each change, to isolate the issue.