Spring JNDI conection Websphere Application Server

My problem is the performance to connect by JNDI DB2 in AS400 - Websphere Application Server

Websphere AS 8 configuration is the same like IBM infocenter explain, my JDBC provider is DB2 UDB for iSeries (Toolbox-XA) with last JTOpen drivers, all datasources are referenced to this provider.

In my spring file the datasource is:

<jee:jndi-lookup id="dataSourceId"
jndi-name="jdbc/databaseName"
cache="true"
resource-ref="true"
lookup-on-startup="true"
proxy-interface="javax.sql.DataSource"/>

but if i declare the datasource like :

<bean id="sicDataSource"
class="org.springframework.jdbc.datasource.DriverM anagerDataSource">

<property name="driverClassName">
<value>com.ibm.as400.access.AS400JDBCDriver</value>
</property>
<property name="url">
<value>*</value>
</property>
<property name="username">
<value>*</value>
</property>
<property name="password">
<value>*</value>
</property>
</bean>

the performance improve 3 times. ¿Whats wrong?¿ I guess that JNDI conection is more efficient than direct conection?

Spring JNDI conection Websphere Application Server - DB2