I need to know the firing order for a 4.3 motor out of a 1990 chevy truck

Usually the firing order is cast somewhere on the intake manifold. Most Vortec v-6's are 165432

Yes, that is true the firing order is cast into the intake manifold behind the carb area and ma0641 is correct on the order 1-6-5-4-3-2

Attachment 34939
This may clear things up for you, yes?