From what you have mentioned I would guess that the shaft is too whippy for you swing. This will cause it to over kick at times giving you a closed club face (pulling) and sometimes it can be left open causing it to carry straight and then fade (slice).

I would say that you need to look for a S-Flex shaft with a stiffer tip to help you with the launch angle and consistancy.

Might want to look at....
Aldila NV 65
AccuFLEX Icon V2
AccuFLEX JLG
Fujikura Vista Pro 70
UST V2 75

All of these shafts will come stable enough to handle your swing but smooth enough for you to feel them through impact.

Let me know if I can help with the reshaft.