What other tables are you using in your report?  Are you using Crystal Reports?

I don't believe that there is a way to add a new key,  however sometimes the way you select and link your data tables can make a dramatic difference.

Tip #1  When linking your tables try to put the table with the most records on the left side of the link.

Tip #2  Try using the Business Insights Reporter to initially create your report then use crystal reports to fancy it up.   This creates a view that the providex interpreter interprets instead of the crystal odbc driver (which is slower).

Correction:  In Tip #1,  I meant to say the LEFT side.  Sorry.

Please note that if the table on the right has a field that is the first group the report will run very slow. If you use the Page N of M feature the report will run very very slow.

Also, since we're talking about speed, its worth noting that any filtering of the report should be done at the record selection level, rather than suppressing detail based on certain criteria. For instance, if you only want to report sales from invoices from last year, set that filter under Report / Select Expert / Record.  

Thanks for the suggestions, I'll re-examine how my query is formed.  Yes, I'm using Crystal Reports, querying the AR Invoice History files, grouped by the Category4 filed of the CI_Item file.  Since Category4 is not part of any key, I'm presuming that's what slows the report.

Interesting comment about the Business Insights, I was unaware of that.

I suspect you are using the Invoice History Header and Detail files along with the CI_Item file.   In this situation the Invoice History Detail file should be on the left and the other two on the right. If you are grouping on Category 4 from the CI_Item you should create a formula with Category 4 as it's formula and group on the formula.  This will help with the speed.