Unless the poster has a newer cast crank external balanced engine a slipped internal balanced engines balancer will not cause a vibration.  Yes, unless it's slipped BAD and is about to come apart/fall off. I mean like the outer ring is wobbling...but he did say it looks OK though didn't he? So yeah, the damper shouldn't be the issue if it's neutral balance. Unless there's an issue w/ the flexplate or torque converter, it's gonna be time to tear into the motor.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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