You might want to find the smallest gif file that demonstrates this problem and forward it to the module author along with the minimal complete script that displays the file. My first guess would be that because you're on a Windows system, the module might not be doing "binmode" on the input file, and whenever the gif file happens to contain a "^Z" byte (0x1a, the text-mode "end-of-file" marker), the input terminates at that point.

Actually, I would be very surprised if this turns out to be the problem -- the binmode/textmode problem is as old as MS-DOS, and Perl/Tk has been around on Windows long enough that this should have been resolved by now.