Do you have pinion angle shims under the spring perches? If you're borderline on the angle, 4 degree shims might be enough to correct the vibes. And you are borderline if just changing shackles caused the vibes to pop up. Or you could ditch the rear lift shackles and go back to stock and see what happens.
But yeah, SYE would be the ideal fix.
Dodge did not build my Jeep.
1988 Wrangler,4.2L I-6, Howell EFI JP-1, 5 Speed Peugeot, Zone 2.5" lift + 1/2" booms, BFG 31 x 10.5, Bestop.