[comptiger5000]

A 4.6 should be ok down to 1400 or so. Probably don't want to go lower, and 1500 would still be ok. The big reason for the taller gearing is to keep enough load on it with the reduced aero drag from the basjoos treatment.

Long tube headers tuned for maximum low end torque, and certain other engine tweaks might help it turn very low rpms comfortably and efficiently on the highway. Big engines are only a true killer around town, on the highway, they just need a very different set-up than small engines.

For example, my grandfather used to have a late 80s / early 90s V6 S10 (not sure which V6) with a 5 speed. He now has a late 90s I4 S10 with a 5 speed. He says that while the V6 had much more power, they both get the same gas mileage on the highway (the 4 is a little better around town), with the V6 doing even a little better in the hills. Basically, for a larger vehicle, a small engine can require such low gearing compared to a larger one that it's no more efficient in steady state cruising.