If I recall the difference between tow and non tow is 3mph, no more.
When ZF made this transmission, their goal was to sell one - and only one - model of it to as many car manufacturers as possible, with the promise of customizing through programming to adapt to vehicule weight, power and cater to AWD as well as FWD variations for transverse applications.
In other words, one transmission with one set of gears for everybody, then let the *client* program them to their specs. ZF had a promo campaign that attracted a lot of attention for this tranny, with its small size, light weight, 9 gears (well...) and AWD capability.
And then we have the V6 Cherokee : as it is now, it's power band doesn't allow highway cruising below 1500 RPM (give or take), so 9th gear is functionally useless considering the fixed gear ratio.
The I4 has a higher final gearing ratio and can chug along at lower RPMs, so 9th is doable below 75mph on flat ground. Same deal for export models with a diesel : more low end torque means 9th can be used more.
If we really wanted to make 9th happen in 3.2L Cherokees, we'd either need to have a shorter final drive ratio, or hope for a Pentastar improvement on low end torque. With a shorter final drive though, overall mpgs would likely hurt...
My avatar is the Elder Predator
(goes well with my forum status and overall temper
2015 North (Canada) - V6 - AD1
Cold, Tow, 8.4A, 9 speakers with sub