Having Problems With Garry's Mod Server - Lag?

Why are you using a maxrate of 2500? Are you running the server on a 2Mbps DSL connection or something? If you’re running this with a GSP, or running it on your own dedicated server / VPS you’re likely going to have at least 100Mbps.

If that is the case use the following rates in your server.cfg:-
sv_minrate 0
sv_maxrate 0
sv_minupdaterate 10
sv_maxupdaterate 66

You’re currently getting choke because players are trying to receive data at the mid - higher end of the update rate but because your maxrate cvar is set so low at only 2500 not all the data is coming through as it should, or is being queued.

Hope this helps.