First, what version are you flying ?
then...
What type of internet connection do you have ?
were , you "hosting ?" or joining ?
try the "shift+z" ping test for latency to host...
I fly missions there mainly, and see those who dont have a clue as to what they have running in the background, in game... stuttering & skipping, from an un-tuned ---system !
Yes you can , TUNE your "connection" , as much as your PC.
http://www.geocities.com/pc_tweaker/main.htmlthere is also a Sound prefix , that helps with some of the stuttering ( the sound files are a BIG part of the sims, and a good sound card makes a world of difference ), but all these things I mention are worth investigating, before you jump to the "mod" conclusion.
if an a/c's file has been "modified", you cant join my games. for the differences in the profiles...
like trying to join a v3.1 patched game , with a stock 3.0 install... simply doesnt work that way.
IM me, if you need further assistance.