One thing to check is that you may be unconsciously opening the club face on the backswing then hanging on to the open club face through impact as you rotate. This is very common. You should feel like the back of your front wrist is pointing down at the target line 1/2 way back on your backswing… keeping the club face square like setup. The club face should be at a 45° angle 1/2 way back… not toe up. This may help your slice.
Ross