played single player for 7hrs straight with internet cord unplugged (No Problems). two days later i plugged cord back in and played connected to xbox live (experienced frequent lag). played like that for about 2hrs. then unplugged internet cord again
from xbox and played for another 8hrs straight experiencing no lag. i also have the game installed on my system.
i have noticed that being singed into xbox live lately has been causing additional problems when playing solo games. all my friends have said im crazy. using a xbox slim console.
My recommendation try signing out of xbox live or disconnect the cord to see if that helps.