Cruising RPM. can it be to low ?

Doen't take too much hp to move a car at highway speeds pretty much lower the better.

I heard lots recommend peak torque before but the makes no sense to me unless you got a diesel that peaks under 2000 rpm.

Say your engine peaks at 3200 rpm yes thats where your engine is most VE efficient.
But going from 3200 rpm to 1600 rpm pretty much cuts the fuel and air in half. Even if your burns more fuel per hp 1600 rpm still gonna be better on gas.

Now 1500 rpm might not be better than 1600 rpm theres lots of variables. But generally lower the better.

Now to me, I don't like my car to lug and have to change gear for every slight incline.

My engine is soft under 2000 rpm and lugs quite a bit. So in town under 40 mph I have to drive in second cause of the 2.94 gears. Which gives me effective gear ratio of 4.26.

If I was to go overdrive I want 55 mph to be at or slightly under 2000 rpm. So I could go into OD on back roads also not just the highway. So at 70 it probably be around 2500 rpm.

So to me it depends where your car lugs.