I'm not sure what issue you been having with Voltaic Slash
VS builds up a stack that adds damage to shock but it also builds up induction that reduces the cost of it
Most deception rotations involve using VS Twice, firing off shock, repeat
Even if your VS buff is still on and you have a boost to damage, in most cases for both pvp and pve its better to still hit VS twice
youll run out of force way too quickly otherwise. I tend to fire off shock without induction but only as a finishing blow or against people i cant catch up to (force speed is down so they are too far for melee but close enough for discharge and shock)
TL;DR: I advise always using VS twice before shock even if the buff is still up