haha, in New jersey on route 80, you are right...that is the norm sometimes!
So another friend of mine and I were chatting tonight and he enlightened me to exactly what you are talking about. Prior to two hours ago, I had never looked into this "starting line ratio" SLR math. I definitely trust you for tech advice Larry and my buddy who was explaining SLR. Using those Wallace Racing calculators I did exactly what you explained.
http://www.wallaceracing.com/calc-slr.php
You are right that the steep 1st gear of the 700r4/4l60 is a big factor. What you said about swapping out the 1st gear in the trans could be an option, but I was hoping not to have to pull the trans out of the car this year, or for a year. I could always do that 1st gear swap next time it ever comes out.
As for highway cruising, I have noticed that when I activate lockup on the torque converter in OD on the highway, it usually pulls the rpms down about 400ish rpm.
So, for example, I took this photo while speedily-cruising on an open stretch of rt78 out in Pa on the way back from the UMI autoX event. I am used to locking up the converter and usually will coast at 85mph and be right at 2,500 rpms with these 3.55 gears. I think I did my math right?? If I were doing 85 mph with 3.91 gears and locked up converter... I would be at 2,753 rpms? If that math is right, thats not bad at all. (cross multiplication and such)
Eventually I would like a set of stickier/taller tires, but for 2021 I am going to use the current 26.1" tall MT ET Street SS tires. If I could find a deal on the old style Centerline Convo-pro wheels, thats what I would drag race with and that would have a tall slick on it. Just not for 2021.