So this is very strange. I have both my Windows 7 workstation, and my new OSX Mojave workstation side by side.
If I print from the windows machine it works fine. I can zero out the margins, tell the printer to expand to minimal, and print borderless. This is an 8.5x11 sheet through the general feeder.
If I do the same exact settings on the Mac... the margins will not go away. I've printed through Lightroom for years now and always had excellent results. The same thing happens if I try from photoshop however... The Mac forces the margins...the windows system lets me print however I want.