motd.txt goes in gmod root. (Think that's it in 3.31)
ulx showMotd must be set to 1 (think it's that by default if you've never edited your ulx server.ini)
If you have edited ulx server.ini, make sure it's edited version resides in gmod/cfg
I believe Gmod now has a motd convar. I don't know what it is. It must be enabled too I'm pretty sure.
Also... why 3.31?
If you have problems with a new version... you really should ask for help.
New versions often include fixes to things Garry has broken, or fixes to known security risks.
Other than a ban file or user file issue when trying to work with players with \\ in thier names, 3.4 is solid.