OK, I see this sort of post all the time, and quite frankly, it confuses me. Why would you list 8500 rows on a parameter listing. This is just torturing your users to search through all those rows to find the one that they want.
One would think that there needs to be a better way...let them type the list with commas and have the report parse the delimited string. Let them select some other categorizing field and display the items in that. Let them enter the first couple of letters of the items that they are after and display all the items that match.
Thinking about it, if they don't know what they are looking for, giving them 8500 choices probably isn't going to help and having them select say 10 from the list is going to be a pain.
I don't know the input, I don't know the data, but humans....