Actually current Solaris tar is large file aware but assuming you are running Gnu/Linux and then Gnu tar, you might want to create a file containing the list of files to archive then use
tar -T list.txt -cvf file.tar
That would rule out a command line /environment overflow.
The file system you use to store the tar file might also causing the issue. For example FAT32 cannot store files larger than 4GB so only about 800 of your 1000 5MB images would fit in a single archive.