I would start with the application server and the database server. Verify the hardware is not a bottleneck (CPU/memory/IO bound).
Is something else running on the server that may be impacting your performance?
Use BEA's performance monitor to determine which kind of requests (which
servlet(s)) are taking the longest. Drill down into the long running requests to determine exactly what code is slow.
Check the servlet
thread pool and the db connection pool. Are they maxed?
I can't give you more specifics because I've never used Weblogic.
But if you check those areas, I think you'll see what causing the slowness and the solution will follow.