[mrnickleye]

The car in question should cruise 77mph @ 3k rpm with the stock 225x50x16 tires. The stock differential gear ratio is 4.3:1

With 245x50x16 (I ran on the back for a year), it was 80mph @ 3k rpm

I suspect you either have smaller than stock tires on the car. OR

You 'lock-up' torque converter is not functioning.

While driving at a smooth, steady acceleration, watch the tach, and feel the shifts. 1-2, 2-3, 3-4, then into lock-up.

The lock-up will drop the rpm about 300r's, and should happen at about 45-50mph. It actually sounds and feels like a slight gear change in mine.

Also, the 1-2 shift in mine is harder than all the rest. been that way for 5 years. I don't like to fix things that ain't broke.