We have upgraded to version 3.0.2 and experiencing very bad performance

We are running replica set and the primary and one secondary is running at 90% Memory which is causing slow performance with our web application

We have even created a new large box (replica secondary) within AWS and it is running at 90% memory

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                                            
25036 root      20   0  131g  13g  11g S  2.7 90.7 108:21.05 mongod  

When we restart the mongo process on the primary and trigger a failover to another secondary, performance improves. However, after a few hours the memory starts to rise and performance decreases.

We are currently needing restart the mongod service on our preferred primary every 24 hours to maintain performance.