Tpump performing very erratically

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Tpump performing very erratically

We are calling Tpump from Informatica to load a flat file. Though no of records of low enough, still it is taking too long a time to load data. Here is list
giving details of no of rows loaded and time taken. Even for as loas as 1707 rows it's taking over 13 mins and then another time for 1468 rows it's taking 12 sec only. Could there be anything I can do to resolve this. We are using 8 session with pack of 20.

No of rows Time Taken
1468 12 sec
3567 21:10min
1188 15sec
2123 6:44m
298 19sec
137 13sec
1707 13:48m
26045 25:27min
25266 18:23min
6552 39:34min

Prahlad