You can start a process in high proirity in command line. Use the start command.
start ["title"] [/dPath] [/i] [/min] [/max] [{/separate | /shared}] [{/low | /normal | /high | /realtime | /abovenormal | belownormal}] [/wait] [/b] [FileName] [parameters]
eg:- start "Explorer" /high "C:\Windows\explorer.exe" For easy access type this into a notepad and save as file with "bat" extension.
cmd /c start "Google Sync" /belownormal "C:\Program Files\Google\Drive\googledrivesync.exe" /autostart