Making it a better driver

What do you mean by doesn't like to cruise over 60 mph ?
Too many rpms or no power or ride or a combination of each ?

If it's no power than OD won't help
If it's power than it probably needs a tune up any /6 I've ever had could do 70 plus even the one that blew the rod out side still kept up with traffic and made it home :) .
And if it is tuned up and don't have enough power than you want a V8, a V8 don't make your car into a race car
most cars now day have over 200 hp. 4bbl 318 with duals and highway gears will do.