Recommandations or Expériences for A/C Duct Repair

Does anyone have experience with someone who can diagnose and repair a/c ductwork? I realize most a/c companies will, but looking for personal experience as I'm trying to minimize destructive investigation (and of course cost).

The house was purchased a year ago, and I did some rehab work on the a/c to where all works well, except I know there is something up with the ducts. A leak (as there is cool air in the plenum) and either a collapsed duct or a hidden damper, as the upstairs blows very hard but much less so downstairs.