There was definitely some tension starting in Season 2, when Tony was elevated, and he moved up Paulie and Silvio equally and had Pussy and Furio reporting to the both of them.

Neither one would have filled Tony's shoes. As BostonGuy17 mentioned, Silvio had panic attacks when he was merely acting boss. And Paulie? New York would have outmaneuvered him and absorbed the Jersey crew in a heartbeat.