With a 4.5 / 5" lift is it a good idea to use a dropped pitman arm to straighten things out a little? Thanks

 

Yes, but totally not needed. Better option would be Over the knucle steering and a trackbar.

 

if you have a stock track bar with stock bracket, then keep the stock pitman arm.
unless you have a drop bracket for the track bar, like the rubicon express hd superflex track bar, then go with a drop pitman arm.

apparently, the grand cherokee pitman arm has about a 1 inch drop over the xj.

you want the track bar and your drag link to be on the same parallel or you'll just get tones of bump steer.