I'm not sure how to help you with this one, because you are doing something that is very unusual. As we have discussed, air shocks / air bags are generally "forbidden" as a way to level the vehicle when you add weight to the rear end - and that is what you keep describing as one of your goals.
If you are going to continue down this path, your first step is to modify the Jeep's suspension to get the tire-to-wheelwell clearance you need, before you add any load. With no weight on the hitch, install the air devices and pump them up get the clearance you need. This is the new permanent position of your Jeep. You've jacked up the rear end, you have the tire clearance that you need, but the headlights are pointed down. So adjust them up to the proper aim, and you are good to go, with or without a TM. My question at this point is why not do this with a solid lift, instead of air devices? At any rate, at this point you can go ahead and use the WDH as it was intended, to provide weight distribution without juggling the rear end height any more.
Your Jeep now has a new definition of "level". Next step, as Scott said, is to measure the distance from the fender wells to the ground.
Now add the WDH and the TM. The rear end of the Jeep will sag - but do not pump up the air devices to compensate! Instead, crank up the WDH springbars so that the Jeep is again level by the new definition, and the headlights are again pointed in the right direction. You can tell when the Jeep is level by measuring the distance from the ground to the fender wells once more. When you've got the WDH right, the front and the rear will both have settled by the same amount, and at this point, the WDH is doing its job. Incidentally, once you've got the WDH right, I wouldn't expect the front and rear to settle by more than 1/2 inch or so. If this matters, then your oversize tires are really too oversize.
I know this wasn't your question, but I'm not sure anyone can advise you because you're trying to so something very unusual (so no one has experience), and you continue to describe doing something that is technically unwise. And it is complicated by the fact that the Grand Cherokee has such a short wheelbase, which makes proper use of a WDH even more important.
Bill
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