HUH!?!
Hi John - I think you mean 4.37GB. You do not loose over a GB!! Plus DVDSP knows this so in the Disc Inspector you can go upto nearly 4.7GB.
That issue is probably more due to non-ClassA media or burn speed rather than capacity but it can be a good idea not to fill the disc to the max.
Of course it could also be a bitrate issue too.
When this stuff happens its good test in more than one player. See if it is repeatable and if it is in the exact same place. If the images are always blocking off of the disc in the exact same place then check the mux. If not then the 1 & 0's are in the right place and it is a media, burning, playback kinda issue so you can fault find that which might require a lower bitrate video or saving bandwidth by using Dolby Digital AC3 audio etc.
Good luck,