It's not a caster problem, no shims required. The steering wheel being off-center is common after a lift as the axle is moved further from the steering box, pulling the pitman arm to one side. The draglink needs lengthened to recenter steering wheel.
I would get a professional alignment and be sure to tell them to recenter the steering wheel.
Get the alignment its only around $45 and it will save you time and money in the long run.
mine was around $150~$180, but i would get as many free alignments as i wanted for 3 years, which i used often, because i installed the lift, then i put the dropped pitman arm, then i took off the dropped pitman arm because of the jks adjustable trackbar, then installed the shims, then took off the shims, etc etc etc (so overall, i got about 8 or 10 alignments, which means about $10 each)