Can lag output change on a HDTV?

Today, I was playing Rock Band 2 drums online onmy HDTV. The other player quit, and my entire system froze. So, I restarted it like I normally would and tried to play Rock Band 2 again. All of a sudden, something felt very different. My previous lag settings were set perfect for my HDTV, and it literally took me 2 years to find the perfect settings. Now somehow, the lag settings felt different. I looked at the settings, and they were exactly the same as they were before, but now the gameplay lag felt different. I don't know how to explain it. The only thing I can think of, is that my actual HDTV is making different amounts of lag. I have a 37" Olevia LCD HDTV that I got for $500 at WalMart on Black Friday 2 years ago. Ihave beenupset with this HDTV and the lag problems with it,but not that this is happened, I am extremely upset. Could someone please tell me what is going on here? I am almost certain that my HDTV is producing different amounts of lag almost every time I turn it on and off, or possibly my Xbox 360 may be producing lag, I have no idea. I just want to know what's going on, and how I can fix it. Please try to explain this to me, I would really appreciate it!!! Thanks.