My CEGMON source didn't work when it went to scroll the screen. Grant's original CEGMON code worked just fine so I suspected a difference between my assembled code and Grant's code.

To find the difference in the 2 KB file I did a CEGMON dump from the monitor itself and dumped it into a file. I then replaced the ROM code with the original CEGMON code and dumped it to another file.

I saved the two files as CSV files and loaded them into EXCEL (actually Libre Office spreadsheet) and compared the two files. That gave me a few locations which were different and I changed my source code to get it to match Grant's original CEGMON code. The differences were in the area of the screen addresses. It looks like the source file I was using was probably for a 2KB screen memory. 

And it worked! No more scrolling problems.

I uploaded the source code to GitHub.