In tuning my 6E (got 16.5MPG freeway last trip, best ever under "normal" conditions) I was playing around with the subject table. I noticed in a bunch of the low temperature cells (at least all the ones with 20 in them, and a few others) any change made the cells revert to "15".
Intrigued, I downloaded this APYP (http://www.tunerpro.net/download/bins/GM/APYP.bin) as I believe it's not what I used as my base bin, and tried the same with it. Still there.
Not often that I'd be in those cells, but if I was, I'd want to be able to play with them.
Probably something simple I'm missing...