Ive never used premier pro, but im guessing, in the preferences, there is settings that control the import quality.
try to find these settings (if there are any), and that will solve your issue.
Be sure the quality setting is set to DV NTSC, and you should be fine.
Otherwise, there's nothing else you can due, since that resolution is what the GL1 is putting out. Although, GL1's resolution isn't bad, nor does it look poor (I have a GL2), so if it is the camera, there may be something wrong with it's output as well.