Low performance vs previous versions

After load testing a webapp running on Jboss AS 7.2 we experienced low performance vs previous Jboss AS versions (AS 5.1).
To isolate the problem a number of parameter have been configured in order to get some performance improvement as JVM parameters including different GC algorithms, threads and web pools...but the performance was still remaining.
We did a load test on JBoss AS 5 vs AS 7 and on a peak load we did a thread dump. In AS 7 we notice 30% of threads on a BLOCKED state vs 0% in AS 5.
Here is an example of a thread in a BLOCKED state:
http-/172.18.22.10:5103-156" daemon prio=10 tid=0x0000000000c1c800 nid=0x71ea waiting for monitor entry [0x00007faa7fcb9000]
java.lang.Thread.State: BLOCKED (on object monitor)
at java.util.zip.ZipFile$ZipFileInputStream.read(ZipFile.java:676)

• waiting to lock <0x00000000aba77790> (a java.util.jar.JarFile)
  at java.util.zip.ZipFile$ZipFileInflaterInputStream.fill(ZipFile.java:415)
  at java.util.zip.InflaterInputStream.read(InflaterInputStream.java:158)
  at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:283)
  at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:325)
  at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:177)
• locked <0x00000000a0829938> (a java.io.InputStreamReader)
  at java.io.InputStreamReader.read(InputStreamReader.java:184)
  at java.io.BufferedReader.fill(BufferedReader.java:154)
  at java.io.BufferedReader.readLine(BufferedReader.java:317)
• locked <0x00000000a0829938> (a java.io.InputStreamReader)
  at java.io.BufferedReader.readLine(BufferedReader.java:382)
  at org.apache.xerces.util.ObjectFactory.findJarServiceProvider(ObjectFactory.java:344)
  at org.apache.xerces.util.ObjectFactory.createObject(ObjectFactory.java:185)
  at org.apache.xerces.util.ObjectFactory.createObject(ObjectFactory.java:120)
  at org.apache.xerces.parsers.SAXParser. (SAXParser.java:140)
  at org.apache.xerces.parsers.SAXParser. (SAXParser.java:125)
  at org.apache.xerces.jaxp.SAXParserImpl. (SAXParserImpl.java:102)
  at org.apache.xerces.jaxp.SAXParserFactoryImpl.newSAXParser(SAXParserFactoryImpl.java:95)
  at _redirected.SAXParserFactory.newSAXParser(_SAXParserFactory.java:122)
  at com.gft.neti.containers.DataContainerSAXParser.parse(DataContainerSAXParser.java:244)
  at com.gft.neti.containers.DataContainerParser.parse(DataContainerParser.java:56)
  at com.gft.neti.containers.DataContainer.toContainer(DataContainer.java:319)

Any help on avoiding threads of being in the state?