I've used Mercon V for about 5 years? and it lasts longer in the Houston heat. A bit cheaper that Mobil 1 ATF because it's semi-synthetic. Smoothed out the shifts some too.

Take off the upper oil cooler line, shove it under the car (after you remove the crappy panel) and stick it in a 5 gallon bucket. The rest is easy. took about 10 quarts before the new stuff started to come out. Start the engine and let it run until it stops coming out. Start dumping the new stuff down the tranny dipstick hole as fast as it will take it. When the clean stuff starts to come out shut the engine off, reconnect the cooler line, start the engine and check the fluid level. Then top off if needed.