Latteral motion, is cornering, shifting side to side. It almost sounds like you're talking about rocking, or rolling, side to side as you drive up an incline, one wheel before the other.
The rear suspension is a 5 link, 4 links and a panhard rod. Also called a track bar.
So there are 3 possibilities:
The Track Bar, which seems to be your problem.
The Front Diff mounting bushings, a common one.
The Sway Bar mounting bushings, another common one.
The track bar is non-adjustable, and it is set at length that will center the axle at stock ride height. Since you've raised the stock ride height, that has pulled the axle off its center slightly. Yes, an adjustable track bar would allow you to change the length and re-center the axle at the new ride height. Most good lift kits will come with an adjustable or proper length track bar.
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