What trucking comp did swift trans recently acquire?

While there really isn't much of a publicly available database on this, the most major buyout Swift Transportation made was of M.S. Carriers in 2000 or 2001, IIRC. Another company they've bought out was Merit. They bought out Fulton Transportation in the early 90s, as well.

Central Freight and Central Refrigerated aren't owned by Swift - they're privately owned companies which are owned in their entirety by Jerry Moyes, the CEO of Swift Transportation (whereas Swift Transportation is a publicly traded company).

DSW trucks are often seen pulling Swift refrigerated trailers - DSW (Digby Southwest) is not owned by Swift - it is a fleet which leases onto Swift Transportation.