I have a 2006 wk with the 4.7. I think the rating is just over 6500 lbs. It tows much nicer then the old zj did, but being a short wheel base vehicle, power wasn't an issue, the trailer persuading the jeep was. I have the factory tow package, and have towed a 1990 xj from the deep south all the way to country hills with a u haul tandem car carry. It was ok, but when we were looking at trailers, I decided to cap it off at the 21-22' mark and keep it sub 4500 lbs dry.
I had my neighbors 5000lb 24' on it last week going around the block, it was dry and I could definitely feel the sag in the rear.
The real test with a trailer will be driving hwy 1 out to the mountains and having that crosswind. I've seen one too many trailers within the tow rating, that have blown off the road with short wheelbase trucks.
FYI, when I was looking into it, I had read somewhere that you can pull a 30' trailer behind a wk. I think that's just insane.
We are now waiting until we get a diesel.