I agree, I think Palpatine was always looking at Vader suspiciously and Vader was always plotting to be the Master, and both were wanting Luke to be their new apprentice.
I think Palpatine would play of Luke's anger/hatred, and Vader would pull at Luke's bond to him as his son. Ultimately Vader won, but for different reasons. He won because he was swayed by Luke's selflessness, and dedication... He saw someone confront Palpatine, to make things right, and saw Palps for what he was... The tinge of Vader that was good saw that. It was very briefly glimpsed on Endor when Vader and Luke had their talk. It came to be when he felt the love and compassion for his son when he needed him most, and realized he could fight back too.