[comptiger5000]

Assuming you have 31" tires, you're geared a hair taller than me. That would have you turning about 1690 rpm at 60 mph. With the auto, different axle gearing, and smaller tires, I turn about 1760 at 60mph. I've found the engine to be quite happy down to 1500 or so (51mph for me), and acceptable down to about 1300 (45 mph). Below that, it's definitely below its power band and mpg drops a little, as it's struggling a bit. Your RPM at 62 - 63 mph is the same as mine at 60, so your comfortable spot being right in that range seems about right. Then again, if you have larger or smaller tires than the 31s I'm calculating with, my numbers will be off a bit.

That struggling range is what the OP doesn't want to reach, as there is definitely a such thing as being below the sweet spot for mpg.