Pontiac Sunbird won't pass Georgia Emissions test

I have a 1992 Pontiac Sunbird with 3.1 V6, automatic trans.
It will not pass Georgia Emissions testing.  It fails
with high NOx.  I was told by local mechanic that
failing on NOx is caused by either EGR valve problem or
bad CAT.  I had a new CAT installed and when I retested
it did improve but still failed.  The engine and
car run fine.  I had a remanufactured engine installed
back in January.  At that time, the car did pass emissions.
The only thing done to it between then and now was a new
fuel pressure regulator installed because the old one died.
Now it won't pass emissions.  Do you think something went
wrong with the installation of the new fuel pressure
regulator?  Back to the EGR valve.  It is the electronic
type.  No vacuum connector.  Just a cluster of about 4 wires.
I removed it and checked for carbon build up in it or where
it mounts and all was clean which I would expect since
it is a new engine.  With EGR off I started the engine
and could feel vacuum pull from where the valve connects
to the engine and also getting exhaust from the exhaust
tube.  Is there a way to test the EGR valve itself?
I connected the wire cluster back and could not see
any change in the functioning of the valve.  As for
the emissions numbers, the allowed reading for NO ppm is 984
and I'm getting 1377.  This is only under the 25/25 Test.
Everything passes on the 50/15 Test.  I was also told by
local mechanic that even though my HC ppm is passing,
it looks low.  The allowed is 136 and reading is 6 under
the 25/25 Test.  Similar under 50/15 Test.
Also, no check engine  light.
I know this is a difficult problem.  Any ideas?