Have noticed changes in fuel grades at the pump myself, primary filters having shorter lifespan. Fuel these days seems thicker and less "diesel stinky" then what we got a few months ago. Can recommend using a little Diesel Kleen additive in every tank. For me the larger secondary filter lasts about 1 year. Primaries about 3 months now, used to be 4-6 months. Otherwise yeah, check the valves.