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Depends on your mechanical background. Not the easiest to learn on but very doable. Don't get in a hurry, get any manuals you can, read the posts here and there are many very good ones. Take pictures as reference and most importantly CLEAN parts and CLEAN work area. Good luck!
I am also doing my first tranny. 5r55e 2wd. Get the ATSG manual it is great for making sure you put all the parts back in the proper order. Your going to need multiple jacks and jack stands. I got mine out without a tranny jack but I haven't put it back in yet. Your going to need some decent workbench or floor space. Here is a great video on disassembly
The exhaust and drive shaft need to come off. I replaced my exhaust and had a junkyard tranny put in mine lil over a yr ago that died so I didn't have to worry about any rusty/stuck bolts (this will probably be a problem with the exhaust). I did the valve body upgrades before I pulled it which didn't fix all my problems. You can do valvebody with tranny still installed. It might be worthwhile to try that before pulling it.
I rebuilt the 5r55e (first trans ever) last year. It lasted only 10k miles before failing again, and I am just wrapping up the second rebuild. Check out my extensive rebuild thread here: http://www.explorerforum.com/forums/index.php?threads/5r55e-rebuild-diy-diary.428970/. The interesting stuff begins towards the bottom of the first page (I suggest reading through it all). I added on to the thread with more info the second time around. There were a few things I did not do (that I should have done) the first time, that most likely caused the premature failure: 1) should have cleaned the cooler lines; 2) should have replaced torque converter; 3) should have disassembled and replaced damaged pump stator (requires alignment tool). I am also adding an in-line filter and temp gauge as well.
It is most likely the most difficult job you will do on a vehicle, that said, not insurmountable. I would also emphasize the need to clean all parts thoroughly with solvent and a brush (or parts washer). I used the ATSG manual, which is a must for a first timer. You can do it without a trans jack, but it is soooo much easier with one - I found a used harbor freight one on craigslist for cheap. First time around I estimate I spent ~80 hours on the job, second time ~40-50 but being more thorough. If I had to do it a third time, probably could do under 30 hours, there is a pretty steep learning curve.