Thank you for a quick response.

This is how I call procedure:

EXEC UnitPricingTrans

@P_PER_START = 201308,

@P_PER_END = 201309,

@P_CO_CODE = '7001',

@P_UNIT_TYPE = 'VEH',

@P_UNIT = 'AUSMV'

And I always run it with the same parameters.

What is parameter sniffing?