I started tearing into one from a 2WD in early 2011 but did not put it back together. I sold a 2000 Blazer 4x4 to a local man and shortly after the trans went bad. It was pouring AT fluid out the front seal. After pulling the trans out and tearing the pump down it was clear the front bushing was walking and this was causing the major leak. I really did not have confidence that I could do this. I purchased a rebuild package with clutches, steels and a whole lot of seals and gaskets. I watched a great deal of videos on youtube. Along with a very good step by step quide I found online (4l60e rebuild manual, schematics and stuff), I was able to put the parts back together and have a functioning transmission.

I would like to share how I was able to get the teflon seals on the pump and the input shaft. Just stretch the old ones out and cut them off, starting with the lowest one first. Cut a plastic soda bottle so you can surround the shaft and slide the seals down over the shaft and old seals. Don't remove the upper ones until you get the lowest ones on first. Repeat for each seal until all are in place. Use the same soda plastic and hose clamps to the size the seals on the shafts over night. It works great and you don't need to spend the money having the local transmission shop put these on for you.

Another tip when putting the transmission back in is to make sure the torque converter is pushed all the way on and rotate it. Take your time when mating the transmission to the engine. MAKE SURE the torque converter spins freely before and after you tighten the bolts securing the trans to the block.