Actually, it is an inverse relationship.
Less opacity from advanced timing produces more NOx
More opacity from retarded timing produces less NOx.

You need a timing check AND a pressure test on the charge air side.

A few more checks:
Boost line to the turbo wastegate is open.
Blown wastegate

 

Just curious. Why are you checking the emitions anyway? Also your truck shouldnt have a cat. The only time our stock 98 12v's smoked is when you mashed the pedel in 3rd and somewhere above 2300rpm it would put out a little bit. nothing major though. However when I rolled the starwheel forword it smoked quite a bit more. Have you checked to make sure its back?

 

All 12 valves except early '94 have cats.
He's probably checking emissions because it's required.

 

thanks for the info guys. i was wondering about the cat. converter. my manual doesn't list it under emissions controls, but i have heard people talking about theirs getting plugged up:

"Check first for a plugged catalytic converter , fuel filter, or air filter
o From: DYNOOMAN@aol.com - I see alot of low horsepower problems due to Excessive idle time's and plugged cat's... About 50%"
from dodgeram.org.

i will try to check out the boost line and wastegate. i also read that the afc spring could be at fault. is that related to the starwheel? i only have one of those Haynes manuals and can't find a section describing the interior of the afc.

btw, infidel is right about emissions tests being required for where i live here in the Front Range

 

If your truck is truly stock, the AFC spring, housing position, and star wheel shouldn't be the issue.
Retarded timing and boost leaks are the most common problem associated to a stock truck with emissions problems.

A sooted cat does cause smoke, but you can usually clear that with loading the engine such as a hard run up a mountain pass

Most boost leaks are hard to find without a pressure test on the charge air side.

 

If you can't find someone to check your timing, PM me I know of someone down my way that can help.