Yeah that doesn't sound right at-all!
For comparison my hemi has a 2" OME suspension kit with ~80,000km on it, no sway bars at-all at the moment, 32" mud tyres, about ~400kg of gear (with about ~60kg on the roof.) and it doesn't rock and roll enough to make someone car sick
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Does it also have some knocks and rattles? Or just a bouncy/rocky ride and instability?
Do you get any weird feedback through the steering?
You probably would've noticed if it didn't have any swaybars if you looked over the suspension. If it does have the swaybars and the bushes and links are very worn, it would make a heck of a racket.
Blown shocks would be my guess if there isn't much noise.
Dunno anything about EFS, but corrugations and hot weather can kill a set of cheaply-made shocks real quick without much visible wear.