For whats its worth both BTS and John Wood say to just drop the pan change the filter and refill every 30k...
I just spoke with John Woods and this is his recommended procedure:
Drain transmission pan.
Remove pan and clean.
Replace transmission pan.
Fill with 12 quarts od Mercon SP even though you just drained about 8 quarts.
Remove external transmission filter canister and filter element.
Tap filter canister for external tap/drain hose attachment, replace canister WITHOUT filter, connect suitable drain hose and place other end of drain hose in catch container OR
Place large container under external transmission filter mount.
Start engine and idle intil trans warms up (about 10 minutes).
When trans-cooler thermostat opens, remaining old fluid in cooler and lines will flow to external filter mount and out. Extra Mercon SP in overfilled case will replace old fluid.
When fluid stops flowing from external oil filter mount or drain hose, stop engine.
Install new external filter element, replace filter canister OR
Remove drain hose from tapped canister, close tap, remove canister, install new filter, replace canister.
Add Mercon SP to proper level.