If not for the tree blocking your path toward Seattle, I would definitely hope for better results from the 7698. It's one of the 'right' choices for your situation.
When both are working correctly, the 7698 is only slightly less capable than a combination of a DB8e or 91XG combined with a Y10713. At this point, it's hard for me to recommend replacement of the 7698.
Besides double checking the correct assembly and integrity of connections in the balun unit, have you checked the performance of the antenna without any amplifier connected?
http://forum.tvfool.com/showthread.php?t=13646
Then there are the basic checks of the cable and connectors for proper assembly and proof that water has not entered the cable(s).