what causes for multiple brake drag

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what would cause all four brakes to drag after replacing all caliper 2 rotors on front wheel speed sensors serviced by gm due to recall this immedietly made problem worse.mechanic and i decided master cylinder would be a good start because abs or brake light has not been on.Changed master cylinder problem remains all rotors getting very warm.Next day service engine light comes on diagnostics scan says abs module,right front wheel speed sensor,brake switch,catylic need help