It is easier to lock an IRS in place to prevent side to side movement, because you only have to locate each wheel assy, not the whole axle. The other big advantage is better ride and lower unsprung weight.
The downside of IRS is that the ground clearance changes with load and the camber also changes with load. An overloaded IRS will eat the tires.
Ultimately there is a reason that virtually all sports cars and luxury sedans have IRS and virtually all trucks don't.
On the Expy, the short wheelbase, P rated tires and low GVWR really limit the size of the trailer you can tow more than the GCWR. I use a Hensley Arrrow to eliminate sway on my truck.
99 Expedition EB
5.4l, 4x4, 4.10 LS, 285/70-17 BFG AT-KO's, Factory Tow with Extra 24k Trans Cooler
Magnacharger with Lightning I/C Pump Mod, WMS Tube, JBA Titanium Shorty Headers, Bassani/Gibson Cat Back Exhaust, Superchip Flipchip, PIAA Superwhites, Autometer Sport Comp Boost/Vac, Trans Temp, Fuel Press in 3 gauge pillar pod, Hellwig Rear Sway Bar, Motorcraft AGSF12FM1F4 plugs.
Current Project - BQuiet Extreme Throughout Truck - going very slow
Coming Soon - Remote Mount Oil Filter and Extra Engine Oil Cooler, Speaker Upgrades.