Here are my numbers. Before smogging I replaced the IAC, plugs, wires, distributor cap/rotor, vacuum hoses. I check my EGR valve and it is good. I don't know how to check the EGR controller though.

My car is an 87 5.0L TPI.

Any ideas on what to check out next?

What gets me is how much the NOX jumped from 15mph to 25mph....

 

I dont think your cat is doing much, if anything. Was the car up to temp?

 

Car was hot.. about 220F.

The NOX at 15MPH is very low, but at 25MPH is very high so I was thinking it was an EGR issue maybe??

 

More than EGR, look at the HC and the %02 way rich.
Possible bad injector.

And the cat.

 

A good new cat, will "mask" most problems, sort of really bad ones.

Mine passed at 170,000 miles, because of the 2 mo old Magnaflow cat, even without a smog pump even o the car. In essence, I have no AI.R. system, just the cat.

Quit chasing little stuff & replace your 20 yr old (if it is the original) cat.