Performance problem with Oracle Directory server virtual server on port 48901 after migrating to version 11.4.1

I have a virtual server that does simple tcp load balancing on port 48901, to two Oracle Ldap servers. When hosting the vip on my ancient 1500s running version 9.4.8 performance of the VIP matches the performance seen going direct to the ldap servers (subsecond response time) but when using a vip on my newer 3600s, running 11.4.1, performance of the vip is on the order of 5 second response time, compared to subsecond reponse going direct to the server. The two main differences that I can think of are the default tcp protocol profile ( I tried switch to lan-optimized, made no difference) and the fact that on the older F5, I am using a "system wide" snat, whereas on the new 3600, I am using a snat pool and applying that pool to the virtual servers. I wanted the flexibility going forward of using different addresses for different virtual servers etc. I thought (slim chance, but I was grasping) I might be having port starvation issues, so I added a couple more ip addresses to that snat pool, but that made no difference. I have moved this vip back to my old 1500s, but really need to find a fix....