I'd imagine 9th's lofty gear ratio would have the engine spinning incredibly slow. Most engines use a mass airflow sensor, vacuum sensor, or both to determine engine load. It's obvious that one wouldn't want to be in a gear too tall from a power perspective, but what might not be so obvious is that if the load on the engine is too high, it can be more economical to run at a higher rpm under less load, too. So let's figure out just how slowly these engines are spinning.
First, we need to determine how far your tire travels in one revolution.
Let's use the same tire size for everything to make life easier as the overall radius will all be about the same.
215/60R-17
Tire Width: 215 mm
Aspect ratio: The tire sidewall is 60% of the tire’s width --> (215mm)(0.60) = 129 mm --> 5.08 inches
Wheel Size: 17 inches
Tire & Wheel Radius: 5.08 in + 0.5(17 in) = 13.58 in
Circumference of Wheel = 2πr = 2π(13.58 in) = 85.33 in.
This means for every rotation of the tire it travels 85.33 inches.
Let’s compare all of the Renegades – automatic non-TH, automatic TH, and manuals, respectively – at 70 miles per hour. First, converting 85.33 inches to miles is 0.001347 miles.
So we can see that at 70 miles per hour, Trailhawks would be spinning at 1800 rpm in 9th, a far more probable engine speed/load for the transmission's computer to decide to go into that gear compared to non-TH automatics at 1550 rpm.
As mentioned earlier, the "Low Range" isn't a traditional, secondary gear reduction as you'd find in traditional 4x4's with longitudinally mounted engines. The Trailhawk simply has a shorter (numerically larger) final drive ratio and starts off most of the time in second gear; low range is simply first gear. The taller (numerically shorter) final drive in non-trailhawk automatics reduces the torque reduction in all gears making first-gear starts the norm, but makes 9th so lofty it can seldom be engaged. So sure, 1st can be engaged when in low range for TH and non-TH owners can get into 9th probably around +80 mph, but this transmission becomes an effective 8-speed automatic for normal, real-world driving.
Though Trailhawk's don't have a traditional low-range, this is honestly kind of clever but you can really only get away with that in something like a 9-speed automatic. Could you imagine if we still lived in a world of 4-speed automatics and all of you automatic owners would have a realworld 3-speed?