If I am the second owner of a car, and I dont know all of the mods that the last owner made... is there and easy way to tell if the gears have been upgrade? or do I have to pull of the pinion cover and look?
You can get a good "ballpark" estimate by doing the following:
Jack up the car. Make a mark on the pinion/pinion snout so you can count the number of revolutions for the driveshaft.
Use a pen or white out to place a mark on a tire/wheel. With the car in neutral, spin the driveshaft by hand one revolution and count the number of times the rear wheel goes around.
For reference, factory gear ratio for 96-98, 99/01 was 3.27. 03/04 snakes came with 3.55.