Did dodge use a posi-trac rear end in chargers challenger etc?

Yes, Dodge used Posi-Trac rear ends in Chargers and Challengers, but not consistently across all models and years. Posi-Trac (a brand of limited-slip differential) was offered as an option on many models, particularly performance-oriented versions, but it wasn't standard equipment. Whether a specific Charger or Challenger had a Posi-Trac rear end depends on the year, model, and the options selected when it was originally built.