I did that on my 99 tahoe, it took about 8 or 9 hours with a buddy who is a good helper, we were very careful because we had never done anything like that before. I do brakes and change oil and tune ups, but not usually something this big. It took time getting under all the vortec stuff - wires and hoses were a pain to get out of the way, but certainly not more than we could handle. The rest of it is removing brackets off the front of the engine for the compressor alternator and steering pump. Getting the intake off is not hard - once you do take the extra time to clean everything so its like new. The real challenge was getting the intake back on once we had set the new gaskets in place. You have to run a bead of permatex along the front and back of the engine block - where the intake meets it - there is no factory gasket there, the bead of permatex that you put in IS the gasket. if the bead is not right it will leak oil. the trick is getting the intake back in without shifting the gaskets or messing up the bead of permatex. its hard because all that vortec stuff is directly above the block. you have to ease the intake in at an angle and then drop it right in place the first time - dont shift it, if you have to shift it more than a centimeter or so you might as well start over because you cant risk messing up that seal - Whew, that was way more than I thought I would write. All that said this is not too much, if you are mechanically inclined - the gaskets and a tube of permatex cost 50 bucks - the shop wanted 650! Spending my sunday getting my knuckles bruised was well worth the 600 I saved.
one last pointer - you'll have to drain the coolant, just cut the bottom radiator hose off and get a new one - you dont want to have the pliers slip off and crimp down on your finger like I did - it hurts and the blood blister lasts for weeks - on top of that, when it happens and you cuss and throw your channel lock pliers out of the garage as far as you can you will lose about 30 minutes looking for them in the yard.
hope this helps
Gene