I don't have any Steam games (or even a Steam account), so I can't help you with specifics. However, here are a couple of questions that might help others.
1. Have you always had this problem, or has it just happened recently?
2. If only recently, did it first occur last week when the Steam servers were hacked?
If both answers are affirmative (yes), then it could well be that Steam itself is still in the process of sorting their servers out and, due to the reduced capacity available, it is inevitable that more lag than is desirable will be present (some lag will always be present). If this is the case, then you should find an improvement in performance (and a reduction in lag) once Steam have finished their maintenance.