Well I still think air volume is the issue.

Sounds to me like you are near the min required.

If you have a Home Depot nearby ( or another tool rental place ) try renting a bigger compressor for a day or two ( cheaper than buying ) just to confirm wether or not it is air flow.

Also I dont think you ever said but ... what are you doing to dry the air?

I am not sure what effect moisture has on a cut, but I know it tears up the tips.

I would do the following BEFORE selling/sledge.

#1 Rent/Borrow a bigger compressor

#2 With the bigger compressor online try a new tip ( in case moisture damaged the first )

I do know that when I felt cuts were going bad and switched tips it made a 100% difference.