I have a 95 Z28 and I have cleaned most of the grounds in the engine bay.
Now the car run's better and shifts better.
There are 2 grounds on each side of the radiator and one under the driver side engine bay close to the sway bar. Also at the ing. coil right side of the coil at the coil bolt, held on by a 14mm nut.
Clean using a wire brush, the screws and the top and bottom sides of the grounds wire bungs. Then after reinstalling them, you may want to spray with a can of paint to seal the water out for corrosion prevention.

 

should be one on the passenger side of the block in front of the starter.