The fronts are the same. You're saying that you can't level your Durango front to back? If that's so, your rear springs must have been beefed up at some point and have extra arch in them. From stock position, if you crank your torsion bar adjusting bolts 8 full rotations, that'll give you 1.5-2" of lift up front. The rear at that point should need a 1" lift.
If you can, take a pic of your rear leafs and shackles and post it. Someone may have made a modification back there and we may be able to tell from the pics