In the last year or so I've read of more than a few GM guys who swapped T56 slaves only to have the new ones fail shortly after (sounds like a bad run). I'm not sure if this would affect the Viper because the Viper slave is quite different though.
Another issue could be slave clearance, sometimes they need shimmed to make sure they get good contact with the pressure plate. You need the slave to be a certain distance from the PP.
Either way this sounds like your hydraulic system still isn't fixed, sorry