Halo 3 and HDTV LAG---QUESTION for someone with TV expertise

Okay, first off I purchased a Vizio 120hz, (reduced lag) 42" HDTV.

-1080p

-5ms response time

I used to play on a smaller, 32" 1080i hdtv. My BR was much better. Now my br missed quite often. ITs like its laggy or something, I disabled all the extra features, yet it still does this

Could this by chance be network related? Im green bar much of the time.

I personally believe it might be cause its just bigger and im used to 32' the tv sits approx 4 feet away from me..

IF anyone can give me any insight, let me know, feel free to asks more questions to help me better resolve this, thanks.

Id appreciate some help...I can link me tv if ud like...but, i need someones perspective...BTW im USING HDMI cables, 24k gold ends