Sorry about the link, Jerry - it is up there, now
I have a ratio adapter that has almost no error at 60-65 mph.
I did Method 1, but I used 5 x 10 measured miles and averaged the results. That adapter is on my Suburban: SM420 4-speed, 3.55 rear conversion, and 31.5" tires.
I will be doing one soon for the 54 we are restoring: Hydra-Matic transmission, 3.55 rear conversion, and 31.5" tires. I'll use a GPS unit for measurements/data for this adapter.
Your cable might have gone bad due to poor lubrication?
