As said, buy 3 quarts. you fill till it comes out the top hole - it should be close to the 2.6-2.7 quart spec. But watch for it coming out the hole, rather than fillling it per some spec.
yeah... i work at grease monkey, and thats what we do when we service any of our man. trannies. just take the check plug out, drain it, insert drain plug and add till it starts spewing out.
dont even bother pulling your shifter off, unless you want to add a bottle of tx7 or somthin like that
Be sure you have the car relatively level if you choose to use the 'fill it til it comes out the top hole' technique. But you can trust these guys - the capacity is 2.7 qts. -- so drain it; take the shifter out; replace the drain plug and put 2.7 qts. in through the shifter hole and you're good to go. Mercon/Dexron ATF - I use Amsoil synthetic.
Almost everybody who makes fluid makes a synthetic version. Amsoil has dealers everywhere - kind of like Amway. Do a google search under Amsoil and your city - see what comes up. But any synthetic Mercon/Dexron atf ought to work just fine. Hard to say if it will make yours shift smoother -- depends on the shape of the tranny and the shifter to some extent. Mine only has about 16K on it, and hasn't been abused at all. Shifts like butter.