Although it might be pointing the obvious but, did you try this:
tail -f /opt/apache/logs/access/gvh-access_log.1365638400 | grep specific.stuff. | awk '' | cut -d/ -f3 | sort | uniq | sort -n | tail -50
I know it is a long command line but it elimibates the creation of the intermediary file. If this is not working for you, could you please tell why, so that you can get more meaningful answers.