Usualy your either burning oil or leaking oil , the oil has to go somewhere.Look for oil spots under the truck and see if you have a leak somewhere , it could be your oil pan gasket , oil drain plug(I had mine changed on my old truck) , or even the main seal.If its burning a lot , then your rings are probably leaking a little more than they should.Also check your valve cover gaskets and see if its leaking up there , as sometimes it won't make it far enough to see a leak.

1996 Jeep Grand Cherokee 5.2 with mods.Hughes Air gap intake , 52MM TB , ford injectors, 2 3/4" lift, Doug Thorley headers , HID headlights with LED , HID fog lights , glow gauges , a few others