Car won't run past 60mph

I'm afraid you have a worn out rear clutch set in the trans. If I recall, forward direct drive is through rear clutches.
If they are at their last gasp, you get exactly this symptom. Other things I've personally experienced that do this are internal pressure leaks to the rear clutch, and once I had a torque converter start sucking air and buzzing. When the fluid got foamy enough, the clutches wouldn't engage until I sat on the roadside and waited for the bubbles to come out.
Good lyck.