I do a 6.5 gal boil. after an hour or so it boils down to 5.5 where I
ferment 5.5 gal, then rack 5 gal to a keg.

i.e. I end up with 5 (give or take 0.1 gal) gallons at kegging.

(Do a larger boil...I think there are efficency problems if you are
doing all grain. if not, and you are doing extract are your beers
ending with a high starting gravity?)