Not sure if your Jeep's 5 spd auto is the Mercedes transmission or not (the diesel and the V8 used the Benz tranny) but if the shift lever moves left and right from Drive to allow you to manually up shift or down shift, that is what is referred to as locking out the overdrive. You would bump the lever to the left and a 4 appears in the shift indicator rather than the D and this means that the transmission is restricted to gears 1 thru 4.
3.6L Engine
When in the DRIVE position, the first tap to the left (-)
will shift down one gear and will display that gear. For
example, if you are in DRIVE and are in fifth gear, when
you tap the shift lever one time to the left (-), the
transmission will downshift to fourth gear and the display will show 4. Another tap to the left (-) will shift the
transmission into third gear.
Be proactive going up hills and downshift manually and keep the revs up rather than waiting on the transmission to decided that the engine is too loaded down, its too late then and you have lost speed. Going down hills, go ahead and bump it down to 4th or even 3rd to control your speed so you don't use the brakes so much.
Charles