I'm 100% sure there is a +/- gear change possibility on the WK gear selector when it's in "D". Just push the shift lever left or right for smaller or higher gear. It should stay in the selected lower gear until you hit close to redline, or if the RPMs fall too low it changes to a smaller gear.
..and no, 4lo is not an option at normal road speeds.
1998 Grand Cherokee 5.9 LX daily driver, 1.75" BB, 32" KM2s, HPD30 Eaton e-locker/D44a stock LSD, 4.56 gears, custom- fabbed tube bumpers and tube fenders,...
1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***