ive never really heard starvation on the 4.0 climbing a hill, the oil sump is towards the rear, i would be more worried on a steep descent.
and yes, your oiling system works off of gravity, the oil pumps job is to suck it out of the pan, through the filter, the though all the oil ports on a motor (crank, up to the lifters, rockers, valves, camshaft) and the gravity pulls it back down into the oil pan.
1977 Cherokee ChiefEdelbrock 1406, 33X12.50, front 1.5 inch shackle lift. AMC 360, th400 Quadra-Trac
2002 wrangler, stock 4.0, auto, 33X12.50 maxis buckshot, AEV Highline Body kit, Ford 9 inch rear end.
Soon to come mods: 4" full traction lift, 4.56 gears, 35X10.50R15 boggers, 35X12.50 cooper st tires, spooled rear end, and much more.