do szechuan peppercorns get stale?
It's impossible to say for sure as senses are subjective, however there may be nothing wrong with it. Sichuan pepper comes from a completely different plant than black pepper, it's actually in the citrus family, and is more aromatic than spicy. You should get more of a spicy, slightly citrus note rather than it blowing your mouth out with pepperiness. If you aren't tasting much they're most likely old, spices do lose potency over time. Keeping spices sealed well in a cool, dry place helps slow degradation, but eventually the flavor will go.