x3, oil is mostly preference. but if your looking to venture, delo is neat because its cheap, but it also depends on your driving habits, style, mileage, and what your truck responds to. for example, if you drive a ton, or lay on the throttle like some of us do, i would highly recommend a synthetic. if you use your truck for nothing special and are consistant on maintenance delo or rotella would be just fine.
2002 crew cab LB7/allison 1000 sleeper in progress
S475 over billet IHI, 45% exergy injectors, stock CP3 (trying to save the rods) Studs, y-bridge, built trans, t case, traction bars, fass 150 w/sump, tuned by Accel Diesel in Henderson Co. and bunch of other small goodies.