Did a 1994 Chevy silverado z71 have posi-trac?

No, a 1994 Chevy Silverado Z71 did not automatically have Posi-Trac (limited-slip differential). Posi-Trac was an optional feature on many 1994 Silverado models, including the Z71. Whether a specific 1994 Silverado Z71 had it would depend on how it was ordered and equipped by the original owner.