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.