Being the furthest thing from an expert on this, it does strike me that you may over gear the motor. Perhaps a nice SM420 with granny low might work a little better. To go from at least a 4.11 or even a 5.(16?) to a 3.38 is a huge jump. And then to go to a 3 speed w OD may just be too much. The SM420 may or may not be the answer, but I just wanted you to think about the question some more.
