here is what my target line reads for the lfs shortcut:
C:\WINDOWS\system32\cmd.exe /c start "runhigh" /high "C:\LFS\LFS.exe"
just be sure you point to the right locations for your machine, they may be different than mine. the last location should point to your lfs.exe, where your shortcut currently points to. this edit changes the icon to the cmd.exe icon, but you can change it back to the lfs one so it will look better at the same place you changed the target line (right click the shortcut -> properties. there should be a "change icon" button. just browse for your lfs.exe).
but if running in high priority didn't fix your problem, it may be beneficial to not run such a high priority as it can take away from the rest of your system.