Ok, so if anyone is still having problems with lag, I seemed to have fixed mine last night. Read through this blog regarding what the problem is:
Is MW3 Lag Compensation penalizing players with faster connections? | Call of Duty 8 Modern Warfare 3
Fast connections get screwed right?
My connection at home is with Novus and I'm consistently at around 20-25mb download and about 8-11mb upload via speedtest.net. So to fix this problem, I slowed down my connection. If your router supports QOS, you can use that to throttle your connection to your ps3. Or you can flash your router using software from
www.dd-wrt.com | Unleash Your Router, which will allow you to throttle your bandwidth. I've throttled mine down to about a 1-2mb connection going to my ps3.
So with that done, I've fixed any lag that I may have had before, especially on ground war and domination. I've played about 3 hours without any lag at all. Finally, this game is playable now.
If anyone wants to attempt this and has any questions let me know and I'll be happy to assist.