for the differentials there are no drain plugs. you have to pull the diff cover for it. on the front you can use a cheap siphon pump to get the fluid out with out unbolting the pig from the beam. on the Tcase, there is a drain plug, sometimes it is just hidden by a steel thing that has a rubber grommit in it and bolts to the back of the case. i think its a vibration dampener but i am not sure.
i posted a few minutes ago to your thread in the introductions forum. with all the little stuff that you will be doing i would highly recommend a chilton manual or haynes manual for your truck. basically its a book that has every possible do it yourself item covered in it. you can get one at most parts stores.
about your L/S diff. i just repacked mine in my 97 with 108K on it. it was so bad before i did it that i could jack the back end up, put my truck in gear with the engine running and easily stop one tire with my shoe. now that i repacked it with some clutchs out of another axle, with it in gear with the engine off and the rear jacked up, no parking brake, i can torque my lugnuts with a breaker bar and it does not slip. it will wear out again and more quickly this time because i used clutches that were not new but it will be fine for me until i put a different axle under there. check out the tech library for the write up on repacking a L/S.
if you want a locker, you have 3 types. automatic, selectable, and solid.
a solid one is either a "Lincon locker" where the spidergears are welded together and to the carrier or a full spool that serves the same purpose and replaces the carrier or a mini spool that just replaces the spiders.
an automatic locker is one that has a ratcheting mechanism in it so that it can slip when your turning and are not on the gas and will lockup as soon as you give it gas. lock-right, detroit and aussie all make automatic lockers. most automatics replace the spiders but one of the two that detroit makes replaces the carrier. the replaces the spiders.
a selectable locker is one that you can turn on and off like the e-locker in your titan. the one made my OX is manual and has a shift lever that mounts in the cab. ARB lockers are operated by air. this means that they need some type of compressor to go with them. E-lockers are electronicly operated. then there is the Ected locker/limited slip which is made by Auburn. this one is again an electric locker but it also has the L/S feature when unlocked.
lockers are not cheap though. welding or spooling is the cheapest but if you have a daily driver then you will not want to do either of those. automatics are about 200-300 dollars and alot of people like them for the price. selectables are really nice but they are expensive both in initial cost , 600-900 dollars and in the installation cost because the gears need to be set up again because selectable lockers replace the carrier. gear setup can be 150-300 dollars.
wow that was a long post. did i answer all of your questions?
EDIT: wow it was so long that two other ppl answered before i did. MAKG confirmed that that thing i talked about on the Tcase is a dampener.
michowski, our rear diffs dont have drain plugs. fill plugs yes obviously but no drain plugs.