Jensen is not driving Baby (1967 Impala) in Tracker (CBS).
I've seen a couple of posts and even several gossip mags saying that it is the Impala from SPN. It's not!
Russell's car (below) is a 1965 Chevy Malibu
They do look similar when glancing at them head-on, but see the difference in the headlights, the grill, and the roof? Also, Russell's car is a 2-door. Baby is a 4-door and does not have the Chevy Super Sport emblem on her front driver's side quarter panel.
I would imagine that there is some kind of clause in a contract somewhere that since the Impala/Baby is so iconic to Supernatural, Jensen is not allowed to drive the actual 'Hero' car he was given in other shows. But that's just a guess on my part.