If you are banging your head trying to get a mail merge Word Document to print a custom page range, try the solution below first before uninstalling the printer, messing with the drivers, etc. The way Mail Merge works is that it sections off your document. Even though it still looks like normal pages, in the background they are actually now in sections.
Go up to File and Hit Print.
Instead of putting 5-20 to print pages 5 through 20, put s5-s20, which means print section 5 through section 20 (which still is what you see as pages in print preview).
That worked for us, hopefully it can work for you!