I took a look at the ebay repair manuals to see if I could identify the manual I photo'd. The layout and font and page numbering in the photo above match the pages photos of Mitchell manuals in listings on ebay, fwiw.

 

Is there a question in there?

Now you can just buy the entire dealer service manual set with everything for really cheap.
Here is the set of 4 for $70,
1999 Chevrolet GMC Dealer Service Manual CK Truck Silverado Sierra Early Edition | eBay

Or the PDF version for $10-$15 (that you can always search and find on that big auction site).
Chevrolet Silverado 1998-2006 Service Shop Repair Manual USB | eBay


Also, not everyone might be aware of this, but 99 was a split year for pickups. There are 99 OBS and NBS pickups. The 4.3 was in an NBS, but if anyone is searching and finds this...

 

Also, not everyone might be aware of this, but 99 was a split year for pickups. There are 99 OBS and NBS pickups. The 4.3 was in an NBS, but if anyone is searching and finds this...

or

The only GMT-400s for 99 were in the Tahoes, Suburbans, Yukons and 2500/3500 trucks

P0161 O2 Heater, but have power & 5ohm element

Day-0 Monday A couple hundred miles ago, my all-stock 1999 Silverado SES dash light came on. Only one code, P0161, both "pending" and "saved". P0161 is O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2). I erased the codes back then. SES has not come back on in the last few hundred...

www.silveradosierra.com

 

I was just giving you an example on the manual. They are pretty easy to find.

Are you trying to find a mounting point, trying to find the ground schematics, are you just posting it so other people know? You didn't really give a reason for the thread, as in, is there a question you are trying to answer?

99 was a split year for the pickups. They made obs/gmt400 and nbs/gmt800 pickups that year. The gmt400 wasn't called a Silverado or Sierra, but that wasn't directed at you (it was in case someone finds this while searching for their 99). 2000, was a split year for the SUVs, GMT400/OBS and GMT800/NBS.