1. Aluminum pillar and glass bed action and bottom metal. --$175
2. Complete action job square and true. --$175 for the action, extra to install barrel and re-cut chamber, 100-200?
3. Check / recess crown. --$45
4. Tune factory trigger.--$25
5. Lap and mount scope. --$40
You can quickly get into over $500 bucks doing this, that may or may not fix your issues. I got these prices from high tech customs in CO Springs, Richie is who i use when i need work one.
I would try the simple stuff first, the stuff you can do. Check the mag box and bolts as suggested, if you have a little torque wrench you can try torque tuning your action screws. If nothing you can do fixes it; i would either sell it or contact winchester. If they have any kind of moa guarantee i may call them first before doing anything else.