In our AutoCad drawing there is no gap but the merged output from the Gerber files shows a sliver of a gap. Any thoughts?
1. I believe the reason for the small sliver is that you have outputted your gerber files to 3.4 inch format. This means that your gerber files are only accurate to 0.0001 inch -- which is most likely the reason for the gap. I would recommend either outputting at 3.6 inch, which is accurate to 0.000001 inch, or try outputting to metric 3.5 format (accurate to 0.00001mm).
2. Also when you have two boundaries aligning against each other, sometime a viewer may display a gap (due to rounding errors in the display), even if there is not a gap in the Gerber.
Let me know your results.