RangeKing

Hi everyone. I've recently replaced my old slanzenger 34 inch putter for an odyssey 38 inch tank with super stroke grip. I'm 6".4 so went for the longer shaft as I assumed this would suit my height,but my putts are all over the place,mainly going to the left.I tend to grip midway down the grip and have moved up and down but to no improvement. Any advice or help would be great.thanks