Lack of a deep trans pan causes the pan to go dry on the upshift from 2-3 and then it kills the clutches. 1-2 will be ok, but it need more oil for the 2-3 especially if you have a shift kit, after market VB or tend to shift at higher rpms.

The clutches do not slip when just driving on the street, only during gear changes which should be nearly instant if you have an after market VB. The convertor is the slip link between the motor and trans, and the clutches should always be locked up. Anyone who tells you differently doesn't have a clue.