that would work, just don't let it run dry. it pumps out faster than you can pour it in. you might have to cut the truck off (or shift to neutral) after each quart or two and fill it back up, then restart. it may also be difficult to tell when the old fluid has all come out. you might just have to guess at when the additional hidden 7-8 or so quarts have come out. you'll also miss the little bit thats sitting in the cooler.
consider this -
when changing fluid and filter, install a universal drain plug for about $5 which makes future changes a breeze.
if the trans has not been serviced regularly, then after about a week - drain, drop, replace filter and fluid a second time. this gets out all the old sludge that the new fluid loosens up.
then change filter and fluid about every year or so or 25K miles and you'll be fine.