I would first slug the barrel paying close attention to how the slug "feels" as it goes down the barrel.
Try JimB's suggestion and load bigger boolits (greater diameter) before doing anything.
Bigger as sized and with paper patch . . . before BEFORE doing any lapping for sure.
I firelap EVERY gun I own, but with a compound far less aggressive than valve grinding compound of any grit and I have that up to 1200 grit.
I have a method I follow and use it for me and it makes me happy, but then I no longer share it.