TCIII -- I think we are in the same situation. I remember reading that you used the 2x5 logo as the base. I did the same. The initial "full screen" is not really full; it looks full because the background is black at that time. Once the "default skin" is loaded, which is white in day time and blue at night, it becomes clear that the logo image is too small.

Someone at FixYa commented that if one can get a full non-OEM rgn (not gupdate.gcd) and load it to the device, it will overwrite everything... Question is where to find it -- garmin certainly does not provide it.