Yeah, what jdkzombie said. It's a frikkin tank. One that's next to impossible to get your hands on. God mode is the LEAST of the sh*t it should do.
It should also be pointed out that, strictly speaking, tanks have NEVER been "god mode" in any GTA game. They took forever to kill, sure, but that's because they were f*cking tanks, and as my old man used to say: there ain't no cops on the planet who're armed well enough to snuff a tank. Tanks in previous games were still capable of being killed, though - if another tank or sloppy driving didn't get you, then you'd eventually get run to ground after twenty or thirty minutes absorbing bullets.
In GTAV, a single chopper with an assault-rifie armed passenger can smoke your tank in a little under thirty seconds. I know there's a lot of feuding here on the forums between grumps who think GTA should be fun, and fanboys who think GTA should be realistic. But that right there, that's neither fun, nor realistic.