Persistence problems

I think you are using this type of persistence, right :?

"Source address affinity persistence Also known as simple persistence, source address affinity persistence supports TCP and UDP protocols, and directs session requests to the same server based solely on the source IP address of a packet. You generally use this type of persistence technique with stateless applications or streaming content (video and audio) as a means to more evenly distribute load."

When you test this you need to test from multiple  sources (you need to have different IP).