First, I've spent the last 1.5 hrs searching for these answers and was unsuccessful.

I have 2002 F350. I use 4wd ~3 times a week. It's early based on mileage, but for peace of mind, I wanted to change front and rear diff fluids and transfer case fluid.

Here are the problems/questions:
I got a suction pump to draw out the old diff fluid through the fill plug without taking off the cover, however, the tube hits the gears and will not go in to the bottom. Can it be done or is cover removal the only choice?

The diff case fill plugs use a 3/8" ratchet to remove (no problem). The transfer case has a very large recessed hex type plug (like a very large allen wrench would work). Is this normal? Anyone know what size tool it requires?

Any specific recommendations on which fluids work well in each location?

While under there, I was looking at the driveshaft to repack it to eliminate "the clunk". Mine is connected with 4 torx style bolts that a regular socket doesn't seem to grip without force to get it on. Is this normal? I don't want to damage them trying to take it apart. Is there a special socket I should use?

My truck was assembled in Canada according to the door (if that matters).

 

For what it's worth I'd pull the covers, if nothing else I'd want to get the crud out of the bottom of the housings (It'll suprise you) and have a look at the ring and spider gears.

As for the big hex head plug, find a bolt head that fits in it and then jam 2 nuts together on the other end so you can use a wrench on it (or weld a nut on)....gotta love free tools

 

10mm allen if I remember right.
My personal truck uses Redline oil in all the gearboxes. Choice of D4 ATF for the trans and transfer case, or optionally Redline MTL in the stick shift only. (You didn't specify what transmission you have. Yes I noticed that your post askes nothing about it but I am writing this anyway. ) No heavier than that. Rumors of burned up transmission using 90 wt. For the axles I have open differential and I use Redline Heavy Shockproof 75-140 Gear oil. I am completly sold on the stuff due to how much of a difference I feel on the freeway. A lot less throttle required to maintain speed. Even at that viscosity.
And yes, pull the covers, there's a lot of metal shavings in there that could stand to be removed. It shows up as a fine gray mud on the bottom of the housing.

 

So, I did the front and rear differentials and transfer case tonight. Took me about 2.5 hours, including cleanup. I am going to write my lessons learned in case anyone else finds this in a search for themselves:

The front diff cover was hard to get off, required 15mm socket, and one 5/16" allen wrench.

The rear diff cover was easy to get off and required a 13mm socket.

The transfer case plugs were easy and required a 10mm allen wrench.

75W-140 synthetic oil for the rear diff is very hard to find (at least in my area). Even the Jiffy Lubes, who were happy to tell me how much a fluid change was) didn't carry the oil. Makes me wonder what they were planning to put into the diff.

All in all, I am glad I saved myself the extra $$ by doing the work myself.

 

I got my 75W-140 at Canadian tire..... It was expensive though...... do you have a limited slip rear? If so, unless the oil specifically states it has the additive in it, you need to put it in...(got mine at the stealer)

 

The bottle said designed for limited slip and for Ford, and based on the cost, I can't imagine that it didn't have it included.

 

I wouldn't worry about it. If you get any tire scrubbing or chatter you can always go back and add a little modifier later. I doubt if you'll need to.

 

Yup, should be good to go

 

Yep. I needed the 4oz bottle of friction modifier. When the rear was fairly warm from high speed freeway driving, and I came to a stop and had to turn left, the rear would grab and hop a little until the truck straightened out. Added the friction modifier, ran it fast to mix it up, and did several figure eights to get it into the nooks and crannies.

Oh, I used Amsoil this time. Last time I used Redline and didn't need the modifier. No big deal, the modifier is less than five bucks at Ford. And yes, the 75W-140 is hard to find. It's much better to find it well in advance and have it on the shelf for when you decide to do it.