XHD Leaf Springs

It's your pinion angle. It was upset when the new springs were installed. You'll need to do a little reading and findout where it sits now and add a shim inbetween; under the rear spring and above the shock mounting plate.
MoPar Performance used to sell them and still might. Unshure of this. You'll also need a pinion angle finder. You can get one from Comp Cams, sumitt or jegs. There cheap.
The MoPar Chasiss book has the procedure for this. Excellent book to have.