Question about Speedo cable

Not likely.

The speedometer cable turns the speedo head unit. One turn at the speedometer transmission pickup equals one turn at the speedo head unit unless the cable is broken. Then one turn at the transmission pickup equals no turns at the speedo head.

In order for the speedo to read fast, the cable would have to make more turns at the speedo head than it did at the speedo pickup on the transmission. That is not going to happen.

Make a trip to the speedo shop if there is one in your area. Or put the car up on jacks and turn the rear wheel one turn and count the turns of the driveshaft. Stock was either 2.73 or 3.08 depending on the year model and transmission type. If the driveshaft turns 2 3/4 turns for one turn of the wheel, you have 2.73 gears. If the driveshaft turns 3+ little more for one turn of the wheel, you have 3.08 gears. Other gears will produce similar results.

and maybe just a speedo that is just not accurate like I do!! I just got the speedo tuned by using different sized tires!