Hai Jayabharath,
Adding to above points... if you check the DTP monitor --> JOb overview --. it will display the back ground jobs associated with this data load. From the job details of the backround jobs you can find the PID/workprocess no -> Goto Sm66 --> search for the PID and now select the PID -->
It will take you to SM51... here again search for your PID and double click on it. now here you can see at which point the PIDs are taking long time. If you are not aware of all these things take help of BASIS and check at which point its taking long time to load. and one more thing check in the batch manager how many parallel processes were assigned for the DTP.
Regards,
Baskaran