Joozey.

Can you try modding your plugin to JUST be a DLL?
Then try it from another application than 3DGS.

Just to see if the lag in IN your DLL,
or in the message queue between it and 3DGS,
or even withIN 3DGS itself...


Another idea...
Try adding a "slight" delay, or dummy message,
between the LEFTDOWN and the LEFTUP messages...