LOL. IF you can't break it loose, what makes you think a cordless impact gun will?

I have a bar from an old floor jack. It's 2 pieces, and about 4' long, 3/16" steel walls. I use that as a breaker bar. It's worked better than my air gun on many things.

Put it in 5th, have someone stand on the gears, find a BIG breaker bar, and MAN UP!