The only mods that can survive to online play are simple, i.e. rapid-fire controllers. Actual mods to the game software or Xbox hardware get an immediate permanent ban as soon as the Xbox connects to Xbox LIVE. It's hilariously easy to detect changes in either of those categories. Modded JTAG consoles are the exception, but those are never used for modding regular online play since they are banned within 30 minutes, meaning a $200+ console is wasted every 30 minutes the user spends modding online.
You're just dying a lot, I suppose. And ranks in Reach mean nothing except for how much you've played the game. Skill doesn't factor in at all, you could be having your pet dog play it for you and no one would be able to tell the difference.
And just for the record, folks, Microsoft seriously does not care about mods unless they present a serious problem with online play (not auto-fire controllers, but stuff like super-jump and god mode, mostly software modifications). They have neither the money nor the drive to hunt down people who customize what they bought. The only case I can think of that Microsoft ever cared about was when someone was mass-selling modded JTAG consoles, and even then they only received a cease-and-desist. If anything was going to happen to people who modded their Xbox 360's or controllers, it would have happened already.