Is there a way to determine the gear ratio in the rearend?

You can get a rough idea.Jack up the rear wheels.Put in netural.Mark D shaft and one wheel stud.Turn wheel one compete revolution and count the number of turns the drive shaft turne.If the wheel makes 1 turn and the shaft say makes 4 turns the ratio is about 4.00.Rocky

If it is a sure grip,jack it up and position the yoke straight up and mark it with a piece of tape.Then place a piece of tape on the face of the tire at the bottom and one on the floor that lines up with the one on the tire.Have someone slowly rotate the tire while you count the number of rotations of the yoke.If the yoke rotates 3 1/2 times it is a 3.55, 3 3/4 times it is a 3.73 and so on.

What if he just counts his rpms in Drive or 4th gear...how many MPH for 3000 RPM, etc. Use a GPS receiver for accuracy.

I am interested in this myself, I am supposed to have a 3.23 and it sure feels like a 3.55 or higher to me.

If a sure grip jack both wheels just off the ground, put in neutral, turn till valve stem is at 6 o'clock, then rotate till stem is back at 6 o'clock & 3&1/2 turns on the ujoint is 3:55. If single track, jack up 1 wheel just off the ground & turn the tire 2 revolutions & count the ujoint turns same as above