I did a search and found the post pasted below. Looks like your a343 transmission will take 16 qts if you drop the pan and do a full flush. However, do your own search for transmission flush procedures on that transmission. There are lots of "do's and don't's" for transmission fluid change and the experience of others will help you.
"Just dropped the transmission pan and did a fluid flush. The truck consumed 16 quarts of Mobil 1 to complete the flush. The good news is that the 2000 a343 with 170k did not have anything in the bottom of the pan that was alarming. Next up is to address some of the old rubber bushings that make up the front suspension."