I've shifted mine at 2K, 2500, 3K, 4K and never seen a single spec of fuel mileage change in any of them. Logic and my mechanical background tells me that the fewer times a metal part goes past another metal part, the less it's gonna wear. I don't mind cruising at 2K if I'm on flat ground with no real load, 80mph is 3K on the dot with my tire size. If I'm trying to merge etc, I'll run it up a little higher but otherwise I shift between 2500-3000 and the RPM and the revs fall back to about 2K. As long as you don't try to pin the throttle when the revs are down I don't think you're going to harm a thing. Easy throttle pressure and let the engine do it's job. It's easier on everything, including the clutch.