Verify your rear gear ratio. The 3.55 ratio is not adding up.
Jack up the rear of the car, wheels off the ground.
Chaulk mark the Driveshaft and tires (with Sure-grip differential), count the driveshaft revolutions per on rotation of the tire.
Should be more like 4.25 driveshaft revolutions per one tire revolution.
4.30 rear ratio
225/50 17
25.86" tire diameter
Let's get that ratio double checked. 50 year old cars, lots of other people have been into it, who knows what the car has been through?
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