I can't comment really but any vehicle I use for towing in the future will always have the biggest engine, I towed with my 98 ZJ and with my 07 WK Hemi and for one the power is not in the same solar system and for another the MPG honestly is not better by much with the 6. Around town they get the same (don't forget the Hemi has MDS), on the highway the 6 gets 18 the 8 gets 16. And that's honest MPG not fantasy.
If you're going to tow at the limit or close, make sure the trailer brakes work perfect and the trailer is well balanced. Depending on the tongue weight, Id consider a WD hitch as well if towing at higher speeds.
I haven't looked lately but what is the mileage difference between the WKII V6 vs Hemi?
2007 WK Limited Hemi QDII
1998 ZJ Laredo 4.0 Selectrac