I think that 2000 rpms at 65 mph would be worse for the engine in terms of lugging. I can go 55 - 60 all day in my K20. My first truck was a 66 C10 which I drove 65-75 on a regular basis.
Most cars that I have driven are within 10 percent of 3000 rpms at 60 mph. Try yours a few times and see how it feels. You may decide that you are ok as is.
