Put some things to rest in one post. The Active Drive II can be towed 4 down and IS a 4x4. Can't tow the AD-I. The Grand Cherokee Quadratrac AND Quadradrive are both towable 4 down. Transfer cases are the same, but the Quadradrive Jeep has limited slip axles. Basically it boils down to this; if the transfer case has 4lo (on a Jeep), it has to have a neutral in the T-Case. The T-Case in N and the tranny in park allows the pump to work.
As far as a Jeep Cherokee being a LOT light than a Grand.....well, Cherokee 4x4 is around 4100lbs, and a Grand Overland 4x4 around 4950lbs. Percentage-wise, about 23% heavier, but both are still 4-5K in weight. I tow a Wrangler JKUR that weighs about 4200lbs and my Overland GC is about 5000lbs...but the Overland is much nicer behind the MH and the MPGs are identical.