You need(should) use a program named: OllyDBG or IDA(If you want to buy).
Then you can find strings withing the "source" of the game.
Then you can find the dvar for the gravity/speed etc.
PS: The addresses are protected with (read) only attribute/protection.
That means you have to change the access attribute. (Speed [in BO2] is stored as int) Think it's the same for MW3.