I am still doing the final tuning on my samurai. After the 8V swap I installed a reed switch in the speedo and now the speedo is reading slow. I am pretty sure it has something to do with the magnets in the speedo gear but I havent had a chance to pull it apart to check. Any advice while I wait for a chance to dig into it?

it's a VSS (Vehicle Speed Sensor; you might want to edit your title)

Has nothing to do with speedo reading.
You may have moved the needle on the pin;/ just re-index so you read correct mph.

Oops. VSS right. Thanks.
Im pretty sure i didnt move the needle however.
As far as i can tell, the speedo works through a magnetic coupling, the faster the cable spins the more the magnetic disk pulls the needle against its spring. I think Thats why the magnet is there in the first place.
Anyway, at stop sometimes my needle rests further past zero than other times. I am figuring it has something to do with the position of the magnet in the speedo in relation to my reed switch.

it's a VSS (Vehicle Speed Sensor; you might want to edit your title)

Has nothing to do with speedo reading.
You may have moved the needle on the pin;/ just re-index so you read correct mph.

X2

Also there is a small adjustment lever on the side of the speedo.  Its very easy to move without knowing you did so.  They usually have white paint on them to fix them in place and to show if they've been moved.  If the paint has not been disturbed just reset the needle. If it has, try putting the lever back where it was.  Either way I'm with ecoast the presence of the VSS has no effect on the speedo reading.

Note: The speedo can be adusted to compensate for tire size (within a very limited range) using the lever I've referred to above. The adjustment, however, has no effect on the odometer.  It will be off by a certain percentage for each tire size over stock.

I looked for that lever when i installed the reed switch and did not see one. I did see a small screw that looked to be used for calibration, it did not secure anything and had been installed only part of the way towards the magnetic coupler.
Ill pull it apart again soon and look again, but i was very careful not to touch the face of the speedo or the needle during my work. Im not saying it is not possible only that it is not probable.

Thought i would share this.

The eddy current speedometer has been used for over a century and is still in widespread use. Until the 1980s and the appearance of electronic speedometers it was the only type commonly used.
Originally patented by a German, Otto Schulze on 7 October 1902,[2] it uses a rotating flexible cable usually driven by gearing linked to the output of the vehicle's transmission. The early Volkswagen Beetle and many motorcycles, however, use a cable driven from a front wheel.
When the car or motorcycle is in motion, a speedometer gear assembly will turn a speedometer cable which then turns the speedometer mechanism itself. A small permanent magnet affixed to the speedometer cable interacts with a small aluminum cup (called a speedcup) attached to the shaft of the pointer on the analogue speedometer instrument. As the magnet rotates near the cup, the changing magnetic field produces eddy currents in the cup, which themselves produce another magnetic field. The effect is that the magnet exerts a torque on the cup, "dragging" it, and thus the speedometer pointer, in the direction of its rotation with no mechanical connection between them.[1]
The pointer shaft is held toward zero by a fine torsion spring. The torque on the cup increases with the speed of rotation of the magnet (which is driven by the car's transmission). Thus an increase in the speed of the car will twist the cup and speedometer pointer against the spring. The cup and pointer will turn until the torque of the eddy currents on the cup is balanced by the opposing torque of the spring, and then stop. Since the torque on the cup is exactly proportional to the car's speed, and the spring's deflection is proportional to the torque, the angle of the pointer is also proportional to the speed. At a given speed the pointer will remain motionless and pointing to the appropriate number on the speedometer's dial.
The return spring is calibrated such that a given revolution speed of the cable corresponds to a specific speed indication on the speedometer. This calibration must take into account several factors, including ratios of the tailshaft gears that drive the flexible cable, the final drive ratio in the differential, and the diameter of the driven tires.

A change in the magnetic field will affect the speedometer reading. Not saying that is what is happening, just that it could.

More research reveals that calibration is accomplished by adjusting the torque applied by the needle spring, or by adjusting the strength of the magnetic field.

More research reveals that calibration is accomplished by adjusting the torque applied by the needle spring, or by adjusting the strength of the magnetic field.

Which I believe is what the lever does that was mentioned before.

absolutely.

Circled in red