Ranger505 - Welcome to DealershipForum.
In my experience most GMs come from a sales background and only have a limited knowledge of how the Parts Department operates. That's not necessarily a bad thing - once you get the hang of the job it means you'll likely be left alone to run your department.
(That's a luxury the New Car Manager, Used Car Manager and F&I Manager probably don't have. )
Concerning a report, if it were me I'd create a one page report that you provide monthly to your GM that details the following:
- Parts Department Gross Profit
- Parts Department Net Profit
- Total Parts Inventory
- Total Parts Inventory over 12 months old
In fact, if you're industrious you could gather the above information for the past 12 months and list it as a graph.
I'm sure there will be others who can share their experiences.
Congratulations on your new job and props for having the good sense to ask advice from others who have already been through what you're going through.