dude,the suit has really nothing to do with anakin becoming vader,the suit is simply a life support,anakin becomes more sinister by the time of the ot for the fact of him loosing everything,padme,his mother,obi-wan,these are all factors that lead to the conclusion that he has nothing but his power,he is sinister becouse of his thirst for power due to palpatine,the only one he truly has left...
I think the only way he will act will be as a result of the betrayal & anger he feels after Palpatine convinces him the jedi are in the wrong anf have been holding him back
like when his mum dies in the sand peoples camp....he was well p***ed
the mechanical vader act will come after the suit has been fitted