At 70-75 mph it's spinning at close to 3000 RPMs. I feel like you should be able to cruise at 2200-2300.
That's pretty typical for an engine of that power/torque.
You want something that runs lower in 6th, you want something that is going to have a bit less power on the low end.
My old 2004 Hyundai Tiburon was pretty much the exact same setup - 186hp, 180 ft lbs of torque, at 70-75 freeway speeds in 6th? 3k rpms.
If you want lower rpms, you want either a bigger engine with more power, or sacrifice the low end torque.
Only so many ways you can mix it up.
My 2012 Shelby GT500 on the other hand, 550hp, 510 ft lbs of torque, cruises at 75 at only 1500 rpms.
My 2015 Audi S4, 333hp, 325 ft lbs of torque, cruises at 75 around 2700 rpms
In the end, on a engine of that size/power... if you want it to be fun to drive/have good acceleration, you're going to sacrifice the efficiency at highway cruising speeds. You can't have both.