I used GPSMapEdit to edit a Garmin IMG file, then I saved the file in .mp format, then I Exported the file as .img format. In BaseCamp the topo map looks perfect, it has all the zoom levels. I used MapSetToolKit to install the map on my Garmin Montana and the map only displays the zoomed-in levels. If I try to zoom out to see a large part of the map, the map disappears. I also tried installing the map on the GPS through the Map Install feature of BaseCamp and also through JaVaWa Device Manager. I'm using the demo versions of these programs, I'm not sure what the limitations are between the demo and paid versions and/or if this is causing the missing levels. I'm willing to buy the paid version of the software, if that is causing the problem.
Any ideas on how to fix this are greatly appreciated. If you need more specific details, let me know.

Odd. I don't have the Montana GPS. I use an older Garmin Map76cx. If you could send me your .img or .mp file I could take a look and check to see if the same happens on my GPS. I do have some experience making .img maps for hiking and canoeing.

Thanks Dan, I just figured it out. The map levels are specified in the GPSMapEdit softwarae.
Can you recommend software for making .img maps?

Glad you figured it out.
I use the cgpsmapper, free version, to compile the .mp files into .img I had work experience using databases, GIS software, and computers so I use a variety of ways to create the .mp files.
GPSMapEdit may use cpsmapper, not sure.