Change the serve grip from eastern forehand to continental is by far the more dificult thing to do in tennis.
This change the swing line, is mandatory to PRONATE, the momentum goes UP, and so on...
The best suport I have found about this is the Doug King serve course from Tennisone.com. You will pay for it, but surely the course will payoff...
PB 10 mid Original @ 48 mains VS gut 52 crosses