A few suggestions.....

Add some Chevron with Techron fuel additive.  Change the oil and go to
a heavier viscosity i.e 20W50 - change it back as soon as the test is
complete ( you dont want to run a heavy oil for long in NY in the
winter).  You can even add some STP oil treatment.  If the truck is
carbureted, lean the mixture out as much as possible and readjust
after the test.

Does NY only test at idle?  If so make sure the truck is at operating
temperature and you will only have to lean out the idle mixture.

If it is fuel-injected make sure that your EGR valve and your Oxygen
sensor are good.  A bad Ox sensor will cause you to fail an emission
test as it is part of the mixture control loop.

That is about all of the tricks I can think of to reduce emissions
from an older vehicle short of rebuilding the motor.

Last Feb my '87 car had to undergo emission testing for the first time.
Here is what I was advised to do:  all filters must be clean/new oil/use
Prem gas and add an Oxygenator to it prior to test/NO codes in
computer(the first thing the tech did was access the computer)/get the
vehicle to NOT before going to the test.  I did these things and the car
passed with flying colors.  If fact the tech said new cars would have
trouble getting similar results to my cars' test results.  Possibly I
didn't have to do any of those things, except for the codes, but last
year was the first year we came under emission testing, so I was taking
no chances even though I maintain the vehicle properly...

Dave S(Texas)