Taking the cover off and changing the fluid probably isn't a bad idea, but if you just want to know if you have gears, try this. Put the rear of the car up in the air, but not supported at the wheels. Put the tranny in neutral and then spin your wheels by hand. Count how many times your driveshaft turns for one revolution of the wheel. If it spins about 3.5 times for one wheel revolution, you probably have a 3.55 gear out back. Get it?
