If gravity is God, what is the difference between the two then? Since you don't know what God is, gravity could be an aspect of God. Gravity could flow from God naturally just as infrared energy naturally flows from the human body. Also, everything could be God, the universe, energy/matter, in that case, God has been studied since the beginning.
It's my job to come up with the equipment to detect God? Most already have them, they're called the five senses.
Since you are having quite a tough time understanding how illogical it is to argue that something barely knowable is different from something completely unknowable perhaps I should put it in another light, what is the difference between a small toy racecar and what I have in a box?
Just because you know some of the characteristics that the racecar exhibits does not mean that what I have inside the box is any different.
If gravity is God then, God must be pretty weak. He can only act on matter, for example, and his influence decreases in proportion of the distance that he is from an object. Certainly, he does not take any active influence, nor does he directly bother himself in people's affairs unless, for example, they happen to jump over a cliff.
If you want to say that God is the universe, you might just as well call God the universe. The universe is everything that is encapsuled inside it - matter, energy, and so forth. By it's very definition, there is nothing outside of the universe, unless you want to go into complex metaphysical speculation.
The difference between the equipment used to detect gravity and that used to detect God is that the equipment for gravity can be used by anyone, and achieve a result, regardless of their original belief. However, the equipment used to detect god depends on all number of nebulous concepts, such as belief, and so forth.
Your analogy about the toy car and the box is quite appropriate, and this is a far better analogy than gravity and god.
For the toy car, I can examine the car, measure it, look at it, and so forth. My seeing it does not depend on what my personal opinion is - it will always be a toy car. As for what is in the box, who knows what it is? Is it a doll? A boat? A car? An electronic game? Indeed, how do you know that there is even anything in the box?