Here is my guess....The Cherokee is now a FWD transmission design with rear driven wheels for AWD/4WD operation. The 8 speeds are RWD designs with transfer cases for front drive. Also, the Cherokee uses a higher rpm, lower torque powerplant and won't lug itself around like a v8. I suspect 9th gear is used for 65mph+ flat ground economy cruising. Any power demand will likely cause a downshift.
Honestly, my 8 speed EcoDiesel GC could use a 9th gear at 75 and higher on flat ground. Lower rpms might yield a slight increase in economy. It feels like 1700 rpm would easily pull it at 80mph. As is, it runs 2100 rpm. There is no 9 speed in a RWD tranny that I know of. Jeep engineers know what they are doing.
2009 Murano LE AWD - Traded
2003 Excursion 4x4 7.3 PSD - DIESEL
1985 Mercedes 300SD - DIESEL
JGC LIMITED 4x4, CRD, MAXSTEEL-BLK/FROST INT, LG2, ORA2, BLK HTR, NAV., CD - DIESEL!
Harley FLSTFI '04