The history of the USPS, and the Post Office Department before it, has been that first line supervisors are usually paid LESS THAN the top 25% of the bargaining unit.
That still wouldn't bring USPS into line with manufacturing, but it'd be a start.
Then we'd start shedding load.
How about Saturday delivery?
I'm having a hard time figuring out why anyone would bother working for the USPS if the private sector will pay so much more for comparable skills.