The "speed of gravity" is the same as the speed of light
See:
https://en.wikipedia.org/wiki/Speed_of_gravity
"over balance" has multiple meanings. The common meaning is more weight on one side of a wheel and less on the other, thus causing an imbalance or overbalance of force that rotates a wheel.
Overbalance can mean your credit card is over its credit limit, but I'm sure that is not what you mean.
Overbalance can mean greater force in one direction than in the reverse direction. Such force need not come from gravity. A twirling water sprinkler has an overbalance of force causing it to spin.
Nature has many fundamental forces. Weights have three basic forces involving motion. One is gravitational attraction. Second is inertial resistance to acceleration. Third is momentum resistance to deceleration.
Addition forces involve friction, magnetism, cohesive forces, pressure forces, etc.
