[KainDaMan]

The problem could be a plethera of possibilities, but I suggest checking for this....

1) G-MAP is in server options [gmaps= comma seperated w/o the .gmap extention added]
2) there are absolutely no npcs in the level with 'loadmap' command in them [in online mode you're supposed to warp directly to the gmap itself rather than the levels {example: level = gmap.gmap x=100 y=100}]

3) in the folder opts gmap files are set with both level and file

If lag persists after that then it most likely would be some stefan error or computer error [either server or your compy]