What a nice surprise. Three subsequent attempts to upload large video files to an iTunes U course site succeeded without a hitch. More surprising, 2 of the files were >400Mb! Huzzah!
This kind of reliability may enable some faculty to upload their own media files, which would potentially provide workload relief for our staff.
Ironically, after 2 years of Apple telling us the problem was not on their end, it appears their upgrade solved the problem. I guess it was on their end after all.