I have very similar problem like you ,started 1 week ago , everything was fine before this time.
In LFS when online playing , it says there is too much lag ( spectating , driving ) screen changing color to black and a little part of the screen appear normal.Then server dont throw me out or kick ,i'm parking and waiting , in this time i can see the realtime data ( new pb of other players , blue flag , yellow flag )
I'm using adsl connection checked snr value , and called service to ask anything wron on my line , but they said its okay and well 36dB SNR is perfect.
After that i used ping plotter and started to log jitter and ping time for server.But its seems normal , not bad.
Then uninstalled LFS and re-install it , tried with patch Z,Z13,Z15,Z17 nothing changed.
Put out my computer and used compressed air , cleaned all fans and all surface.Then formated it and install new fresh windows xp 32bit ( sp3 )
Again installed LFS and logitech profiller 508 only but nothing changed.
When i play it offline mode , training mode in my pc FPS is over 200 and no freezing no lagging sure.And checked graphic card for overheating , after 1 hour race , it didnt passed 80c.CPU temp also normal.No overclocking before.
Now today i'll test with splitter device , to reduce unwanted signal on my line ( if there is ) If again no certain solution , i'll try to load cfosspeed program for traffic shaping.
http://www.cfos.de/speed/cfosspeed_e.htm
I have already missed an event ( owrl race 2 ) and dont want to miss more :schwitz
16h race is coming )
Any idea ?