Corsair Force 3 went from 7.8 to 7.4 on WEI?!

SSD performance can vary in WEI. Overtime the ssd will slow down, but I have also run WEI on a couple of different SSDs and have found that the ratings can move between .1 and .4 up or down.

Do you know how to get it back to 7.8?

WEI really doesn't matter...

WEI is completely meaningless. SSDs slow down as they fill up. That's just how it works. You wouldn't even notice if it weren't for that silly wildly inaccurate number windows is telling you.

Agreed. On my laptop I did a clean install WEI went from 7.7 to 7.4, and a week later it went back up to 7.7. WEI doesn't really matter.

check the bios make sure hard drive is not set to ide.

check your SSD firmware version and see if it is current. Lots of bugs in various firmware versions. Sometimes you can provide power to a SSD and not boot your OS. When the drive goes idle it will run its built in clean up routines. all depends on what firmware version you have.