If you pull the plug on the pan, how much tranny fluid do you drop? If I replace the external filter and replace what has drained with synthetic..would that be ok? I am considering doing this once annually over the next few years ..instead of having to get it in the shop and have it puged..what dya think??

With the stock pan, the pan capacity is 7.4 qts, with a system capacity of 12.7 qts.
See link below, with a complete flushing procedure, which does a better job, but requires a little more work.

http://dieselplace.com/forum/showthread.php?t=28690

Nice to have a drain plug on a tranny pan!! ive only got 12k miles on her but haul heavy and hilly here in new england. A dedicated pull rig for my fiver..works hard in summer pulling vermont grades eetc...so figured i would change tha tranny filter once a year...and this year drain the pan and refill w castrol dex3 ...cant hurt right ?? thanks for your input on the capacities..you can look all over the op manuals and never find it..