74 Duster 408 Daily Drivability with 3.73 Gears Vs Stock 3.21 Question.

You realize that even 3.21 rear gears will give you a lot of cruising rpms at interstate speed by today's standards. With 26 inch tall tires, no overdrive, 70 mph is around 3,000 rpms, 80 is roughly 3500 rpms, etc.

Of course, back in the day, when I was young and impatient, I used to cruise at 80-90 mph on two lane roads with 3.23 gears. Now I don't even drive that fast on interstates. It's all what you're used to.
If you don’t go 80+ on the interstate here some asshat will be 12” off your bumper in a monster truck . Even on my motorcycle! I prefer 65 unless I am traveling 100s of miles .