what options do i have dealing with a chimney downdraft
The first thing to check is. Do you have a backflow preventing Cowl on the Chimney. These are quite effective in preventing backflow into your chimney. 



But the real problem is that you are getting a high pressure against your second story wall which is butting against your chimney pipe. Its a natural progression that the wind buffeting the wall will want to flow down the chimney.  Besides the chimney extension to a point outside of the high pressure zones created by the building structure. you could possibly put an elbow on the current chimney to move as far away from the wall as possible.