upload speed issue using RAS

This does not look to be a F5 related issue. Your F5s, and servers, should be connected via a LAN, with same speed for upload and download. Most Internet connections don't have the same speed for download and upload, with upload normally around 5% to 10% of the download. Your VPN users most likely don't have the same download and upload speed. Some companies do have symmetric Internet access, same download and upload, but is a more expensive option. Concluding, investigate one user, check his connection and your company connection.

This site is good Internet test:

http://www.speedtest.net/