Stiffer rear springs?
What are you using to lift the rear? If you've already got the add-a-leaf in there from the Skyjacker lift, that should be pretty stiff. You can also throw in the leaf packs from a 4-door instead, which will be slightly stiffer (and even more so with the add-a-leaf) with the extra spring and even give a little more lift.
If you're looking to reduce body roll, poly bushings along with good shocks (Bilstein, KYB Monomax, KYB Gas-a-Just, Edelbrock, Rancho RS9000, etc.) are your best bet.
Energy Suspension makes a full poly bushing kit just for the 91-94.
You can also get thicker sway bars, but that's quite an expensive option.
You can also throw in the rear sway bar from a 95+ Explorer, which is much beefier than the stock 91-94 rear bar. This reduces body roll, but also has the effect of making it slightly oversteer rather than understeer. You'll also need bushings for a 95+ explorer to install it.