Xbox Live Lag issues

Alright I have had this problem for a long time now and its really starting to make me mad.  When i try to play any of my games online now my xbox decides to lag so bad that I can't even play.  this has only been a problem recently.  I tried to figure out why my connection was so bad and why my games lagged so much online.  So I decided to check my internet connection because thats usually the problem.  In this case its not.  I do run a wireless adapter and I bought a new one thinking that was the problem but no it wasn't.  Then I decided to take my xbox into the same room as my wireless access point, but the result was still **** lag.  Another thing to mention is that my brother who also runs a wireless adapter on his xbox on the same internet connection doesn't experience any lag when he plays.  So I decided to play my games on my xbox in the same place but it was still laggy.  then I played my games on his different xbox in the same spot and voila!  perfect online game play.  So I think there is something wrong with my actual xbox which is causing this issue if any of you guys could shed some light on this i would greatly appreciate it!