here are some pix of what my TB looks like
its pretty damn black in there
http://www.texastruckscene.com/pictu...&pictureid=856
http://www.texastruckscene.com/pictu...&pictureid=855

 

I just recently took off my dad's TB on his 2000 silverado with 40k on it and it was pretty dirty. Looked alot like your TB from the outside but once you look inside you will be amazed by how dirty it is. It was nothing compared to my 2004 silverado with 55k. I'm guessing if you look inside the manifold you will probably see a puddly of oil sitting on the bottom of the manifold from the PCV system. As for achieving good MPG-slow takeoffs, regular maintenance, and good tune.

 

so just go get some TB cleaner and go from there?

 

Definitely take your TB off and EGR system off the manifold (only one bolt, and be careful not to bend the EGR tubing to much) and try to clean the inside of the manifold as much as you can. This might be overkill. But if you go so far you might as well go farther and do the job completely.

 

While it's off, you should get a throttle body spacer too

 

After you do all of that get a tune.
i'm getting 16-17mpg with my 5.3 ECSB with mods in sig.

I can do better than 17 if I stop leaving for work late.

 

i just sprayed the valve and open the valve and sprayed all inside and let it soak til it dissolved and closed da valve started it up
it bogged off the start but almost immediately returned to perfect idle and ever since then idles just right and i got my throttle response back and i can definately notice the difference
i used b-12 chemtool throttle body cleaner from autozone-costs 3 bucks for a 160z can of it

 

16oz i mean**