Could it be the filter or MAP sensor causing a 1992 Blazer with a 350 to keep stalling?

This is something that will drive you nuts. We had one that almost DID drive my friend nuts over. There is no "check engine" light, he replaced everything related to the engine, and it's control devices, and at the end he was ready to start yanking wires. It's symptoms almost mimicked a vacuum leak, but at other times it would run just fine.

Change the fuel filter first. This is the least expensive. If that doesn't correct the problem, and if everything else has been maintained, then I would say replace the map.