SSIS Lookup giving wrong results

I am using SSIS 2008 and I am doing a lookup on a customer table which has like 50K records . I am doing a lookup on the Firstname , lastname & addressid .

In both Source as well as Lookup query

for Firstname & last name lookup columns  I am using lower , ltrim , rtrim  & isnull functions like this lower(ltrim(rtrim(isnull(firstname ,'')))) .

I am doing a Full cache ( as I am doing lookup on 50K records ) .

I am getting duplicates ( I am already having this customer  Firstname = A  , Lastname =  B    addressid =  12345 , again the lookup does not find a match because I get it as a , b , 12345 ) . When I go back to test this record and put a where clause to filter only this particular record it is working fine .

Any help will be greatly appreciated

Thanks,

shek