I am stapling through the tongue. I agree, a 18 gauge staple would be great. But, the gun only shoots 20 gauge. The next flooring stapler I could rent shoots 16, and that is too big for the flooring.
I had turned up the pressure to the gun a bunch of times. It just didn't work.
In any case, I worked on it again last night. I predrilled and used 3d finishing nails on it. It wasn't much faster than the stapler, but it also wasn't as frustrating as there was no dinking around with bent staples. We worked on it for about 5 hours and got as far as shown below. It looks like two more good nights of working on the floor to finish it up.