Yes! It cannot read more than 1,000 songs at once, so if your tunes are not split into playlists, it cannot read them all. If you select a playlist that has 999 songs it will read them fine and then select the next playlist with 1,000 or less songs, it will read them fine as well and so on.
OK.....so where did I go wrong?
I just bought a brand new 8GB Transcend SDHC Card with shipping for $47.48.
I installed Media Monkey and loaded 1116 MP3's from my Itunes Library.
I created 2 playlists. I put songs 1-560 in the 1st play list (560).
I put 561-1116 in the 2nd play list (556).
I transfered the 2 playlists to the Zumo 550 and it showed X of 1116 as it was transferring.
*note get an extrenal card reader to transfer larger amounts of data. Trying to transfer to the card through the Zumo was taking about 10 seconds a song, or so it seemed. I canceled after 60 songs as I needed to leave and wanted the GPS. I decided to re transfer via the external card reader while I was gone. It transfered about 1 second a song, so I waited to leave.
When the transfer was complete, I put the card in the Zumo. It showed 1 of 1000.
I went to the playlists and playlist 1 showed 1 of 560.
I went to the 2nd playlist and it only showed 1 of 440.

Well 560 + 440 = 1000
Steve