Ignition key stays in "start" position - doesn't spring back
After researching for about a week, I had a lot of conflicting info about where the return spring was located. Long story short, I finally figured out it is in the electrical portion of the starter switch. The image below shows the ignition module - this consists of the ignition lock cylinder (where the key goes in), the lock cylinder case assembly (the cast aluminum block in which the lock cylinder is housed), and the ignition switch itself (the electric switch that plugs into the bottom of the housing).

Here's another view from the top:

Before I get into how to replace it, I want to add my "disclaimer" (sorry, my lawyer said I have to)

I am NOT a "master mechanic," or "expert" on repairing Chevy trucks. I am, however, a pretty decent shade-tree mechanic who's been busting my knuckles on about everything that rolls since I was a kid. I may not have all the "tech" knowledge, but I know how to improvise, use common-sense, and get the job done. I'm also not a professional photographer, so sorry for the lack of pictures. I didn't have a photographer standing by when I did this job, so I just got the main parts when I had a second. I didn't photograph the simple stuff, like lower dash cover and steering column covers. I will, however, explain a few tips to getting these off easier. That being said, don't be too hard on me for lack of more photos.
Here's how it went:
1. Start by disconnecting the negative battery cable (always a good start when working on electrical components).
2. If you feel it necessary, research how-to, and disable the SRS airbag system. I did not, since I wasn't going to be removing the steering wheel or working around any of the pressure sensors. Some may think I'm crazy, but I am careful. If you are afraid of an airbag deploying, by all means DISABLE it!
3. Remove the lower dash trim panel beneath the steering wheel. There are 2 screws on the bottom (7mm), and 2 panel clips on the top. PULL IT STRAIGHT OUT FROM THE TOP, NOT DOWN, or you will break the clips.
4. Once the lower panel is off, you will see the knee bolster (see photo below). Remove the 4 10mm nuts and it comes right off.

Knee Bolster. Note the 2 nuts on the left side - 2 just like it on the right. Have to take this off to get to the harness connector.
5. Remove the tilt steering lever by pulling it straight out. Might have to pop it out with a pry bar (what some people call a "screwdriver"), but once you get it past the first detente it comes out easy.
6. Remove the lower steering column cover by taking out the two 25mm Torx screws from the bottom. Tip: Tilt the steering column all the way up to do this; makes it easier. There are two "hooks" on the back of the shroud that attach it to the top cover, so wiggle and jiggle it (technical mechanic terms - sorry) until it comes free.
7. Many sources I have found (including Chilton's) said the top cover should just "lift straight up and remove." ...Wrong. Maybe on some models, but not the 2000. First, tilt the steering wheel all the way down (use the handle you just removed, just don't stick it in all the way)

Secondly, there is a Torx screw holding the top cover on that has to be accessed from underneath. It's actually like a "reverse" Torx screw; a head that looks like the end of a Torx driver. Use a 4mm socket and it fits perfect. The screw is right behind the lock cylinder housing on the right side (next to the steering wheel). Remove this screw and COMPLETE STEP 8 before attempting to pull the cover off.
8. Before pulling the top column cover off, remove the dash trim bezel by prying the clips loose (use your fingers, they're not hard to get off). This is the bezel that surrounds the instrument cluster and radio. Putting the truck in 1st gear (on a column shift) makes this a little easier. This will give you clearance to get the top column cover off easy.
9. Now that the column covers and knee bolster are off, you have access to the harness. There is a mesh cover over the wires leading to the harness plug (right behind the knee bolster on the left side). This is velcro - tear it off, you can replace it when you're done. You'll also see about 2 or 3 small zip-ties holding all the different bundles of wires together; clip these CAREFULLY and remove them. Definitely make sure you don't accidentally clip the YELLOW air bag wire!

Note the harness connector on the left side of the picture. See the yellow wire? Be CAREFUL with that! (i.e., AIRBAG).
Once the wires are free to move around, you can unscrew the retaining screw in the middle of the harness connector (9/32 I believe). When you pull the connector free, you will see it does NOT look like the harness you just bought! Have no fear -- There are two connector blocks attached to the main harness connector on each side; one is gray and one is black. To remove them, slide a small screwdriver in between the main connector and the side connector, pry out slightly to release the locking tab, and the two connector blocks will slide right off. Be sure to make a mental note of the orientation of the connector - heavy red wire to the bottom. The side connectors only go one way - they are different sizes so you can't reverse them!
Unclip the plug on the back of the fuze box - this is a squeeze clip. Just pinch the clip and pull it out. There is one other small connector in the middle of the harness (cruise control, I think). Pry the clip apart and separate the plug.
10. Now that you have freed the wires and removed the main connector under the dash, it's time to remove the ignition switch. Right above the ignition switch, in the housing, you see two small square openings on each side of the housing:

Use two small screwdrivers or punches to depress the spring tabs in those holes to release the switch. Disconnect the two wires on top of the ignition housing.
BE SURE to NOT rotate the gear on top of the ignition switch so you can examine it!
11. Now that the switch is out, you can see the gear on top. You will probably notice some damage (I did on mine). To fully remove the harness, disconnect the plug in the middle of the harness and the one on the back of the fuze box.
Here's a shot of the two switches -

12. The easiest way to re-install the switch is to rotate the key in the ignition to the "accessory" position (fully counter-clockwise). Then, rotate the gear on the top of the new ignition switch fully COUNTER-CLOCKWISE (as you are looking at it like it goes in the slot). This way, you will not be off one or two teeth when you put it back in.
13. Re-install the harness. Start by inserting the two additional connectors in the harness connector (the one with the screw in the middle). Then, plug the connector in under the steering column and tighten the screw. Plug in the connector in the back of the fuze box to the left, and the small connector in the middle of the harness. Now you are ready to insert the switch into the bottom of the housing.
14. Make sure the key is in the "accessory" position, and the gear on the switch is rotated all the way counter-clockwise. Insert the switch until you hear the tabs click into place. Connect the two wires on the top of the lock housing.
15. Reconnect the battery and test your installation before putting all the covers back in place! You will know immediately if your switch gear is not aligned.
16. Once you are satisfied that the install is right, zip tie the wires back together like they were when you cut them. Wrap the harness with the mesh covering and re-install the column covers, knee bolster, and trim panels.
The key to this project, like many others, is attention to detail! Note the position of EVERYTHING! Wires are routed a particular way for a reason - you have moving parts in the steering column (tilt, shifter, etc.), so you have to be certain things aren't going to bind.
If you have any problems or questions with this procedure, pm me. I'll be glad to help you the best I can. Good Luck!!