The EGR Modulating Valve
Is the black plastic can attached to the EGR valve
by a larger black heat resistant hose (this is the backpressure sensing port)
And smaller vacuum hoses,
Plus an electrical connector.

On a Ram pickup it is on the passenger side of the engine rear.

On my 1995 i bought a spray can of Chrysler's
"Combustion Chamber Conditioner"
Pulled off the spray head
And pressed in a spray head from another spray can
That allowed me to spray through a small red extension hose (like WD40).

I then made the red extension hose twice a long by slipping on a slightly larger extension hose.

With the engine off i maneuvered this long extension hose down through the throttle body and worked it into one of the two left and right EGR discharge ports that are just below the twin butterfly plates. I sprayed and filled up this passageway cast into the aluminum "Beerbarrel" intake manifold.
(If i did this again i would have the pickup parked slightly uphill)

I waited 30 minutes to loosen up the carbon deposits,
got everything out of the way and started up the engine.
An impressively large cloud of black smoke came out the tailpipe for about three minutes. i suspect part of this black smoke was the Combustion Chamber Conditioner's secondary cleaning of cylinders after it got sucked out of the EGR passageways.

So much black smoke came out that i decided to repeat the process.

The second time the black smoke stopped after about a minute.
A neighbor walking by asked
"What in the world is wrong with your truck?"

I still had part of the can of Combustion Chamber Conditioner left,
so i pulled the backpressure hose off the EGR Modulating Valve and filled up that internal passageway, which the FSM shows going over to the EGR valve, up about an inch, and then down that metal tube over to its connection fitting to the passenger side exhaust manifold.
More black smoke after start up.

When you go back for the emissions retest, it might pay you to buy some E85 fuel and make a blend in your tank. 25 to 33% ethanol would probably reduce the NOx. Drive the truck for 3 to 4 hours so that the PCM computer's two memory positions called AFF and AAF "learn" the new blended fuel. AFF is the "adaptive fuel factor" for short term changes. AAF is the "long term adjustment" called the added adaptive factor.

There is a chance that this ethanol rich blend would partially dissolve some "gunk" in your tank and possibly load up the sock filter at the bottom opening of your submerged fuel pump/pressure regulator/gas gauge sensor unit. If your pickup has the original 1993 factory unit that sock filter may already have quite a bit of junk that it has caught over the years.