Here is a checklist for poor performing reports in AX:
Start by analyzing the query:
1. Do the joins in the query make sense?
2. Are all of the table in the query resulting in index hits when executed, or are there table scans?
3. Are there missing indexes requested by the index advisor? If so, evaluate the difference.
Are the reports written in best practice?
1. Query returns filtered results, not using the report to filter the results, when avoidable.
2. Should the report be converted to RDP if query is expensive?
These should send you down the right path. Chances are high the 9 million rows in InventTrans is not your performance problem.