Cisco Router: TFTP Gets Extremely Slow

A few days back, I had this phone system die.  It was a Cisco UC500, and it was in a continuous reboot.  To make this long story short, I basically grabbed whatever equipment I could just to get something operational for them for a phone system.  One of the things I had to do was to TFTP the IOS, phone system loads, etc onto the flash card.  Well, right about 20%, I started getting timeouts increasing on my TFTP server.  The TFTP started crawling at this point.  Well, Im not one to wait around, so I restarted this TFTP and the second time it worked fine.  Why did that happen?  I have no idea, but I have seen that many times in the past.  I have always jut restarted the TFTP and usually, it works out the second time.  That was with my laptop directly connected to the router.  Go figure, but if you run into that problem, just restart the TFTP again.