Why's my server lagging?

List of plugins:

Code:

BorderGuard.jar      MinecraftRKitPlugin.jar
Essentials.jar       MobDisguise.jar
EssentialsSpawn.jar  Modifyworld.jar
Factions.jar         PermissionsEx.jar
FalseBookBlock.jar   Permissions.jar
FalseBookCart.jar    rawcritics_ore_obfuscation_plugin.jar
FalseBookChat.jar    runecraft2.8.1.jar
FalseBookCore.jar    VanishNoPickup.jar
FalseBookExtra.jar   VirtualChest.jar
FalseBookIC.jar      WorldEdit.jar
iChat.jar            WorldGuard.jar

CPU Usage not more then 25%, Memory not more then 50% usage.
All plugins up-to-date. Though not everyone is made for 1185. May some plugins from the list above cause it?
Servers not crashing, but tickrate is sadly 3.5TPS.
Ping is fine too.

 

Please view this link with info about what causes server lag.

http://wiki.sk89q.com/wiki/Minecraft_server_FAQ

 

speedtest.net

what is your upload speed? and how many players are u running your server with