I just finished installing my floor, 1100 sq ft of engineered reclaimed heart pine. The installation was tedious but the real job was in leveling the subfloor. The advice I got from this site helped a great deal. I was ready to hire the job out and had 6 contractors come out for bids. Not one of them was willing to truely level the subfloor. One of them actually said not to worry about it.... "we install over uneven subfloors all of the time". Antother was willing to sand down one (of about 10) high spots for $1000.
At any rate I took the time to sand down the high spots and then filled the remaining low spots with shingles and felt paper. The end result is amazing, the floor looks absolutely fantastic.
Also, I used the Spotnails stapler with 1.25" Senco staples. That was another suggestion from this site. Worked like a dream.

Thanks again.

Outstanding! Post a picture or two if you would please. They help add to the 'feel good' of this forum.