I have the 913D2 and my coach put an ACCRA tour stiff shaft in it. 

I am 71 and play on hard pan dessert courses in Phoenix, AZ. (lots of roll both in and out of bounds).

I get good distance (225-265) but it is a lot of work and I have a bad back.  The ball goes straight but I cannot draw it whatsoever and have tendency to block. 

Swing speed is 75-80 mph.

I am considering putting a senior flex shaft in which might help me draw the ball and certainly take less work.

Does anyone know if Titleist has a senior or "A" shaft (mid-high) that you believe is an appropriate substitution for what I am trying to accomplish (easy or slower swing and draw capabilities.)?

Thank you

Ken