Saying a filter only traps 2 microns is only part of the specs. You have to know the efficiency or beta ratio at that micron as well. It could be 2 micron at 95%(meaning it traps 95% of the particles that are 2 micron) or it could be 2 micron at 99% efficiency. Generally, as the micron size increases so does its efficiency at that micron. For example, a filter may be 90% efficient at 2 micron, 95% efficient at 3 micron, 98% efficient at 4 micron, and 99.9% efficient at 5 micron and above.
You also have to know what ISO standard the micron test was performed with and whether it was just an efficiency test or beta ratio test which is more accurate.
The primary job of the Parker/Racor chassis filter that comes stock on the 2013 is not to capture the the most micron particles as possible. That is the job of the engine mounted fuel filter. As per my Parker/Racor rep below(who worked with Cummins/Ram to make the factory) the primary job of the filter before the engine is to protect the engine filter from finely dispersed water from the tank. Too much filtration before the engine filter could cause issues and "cheap insurance" becomes "wasted money" when it is not needed.
EDIT: I do know that the 2010+ upgraded NanoNet synthetic media engine filter is a 99.9% efficiency at 4 microns while the old cellulose media one was 98.7% efficiency at 4 microns. I can call some of my old friends at at Fleetguard/Cummins filtration to see what it is at 2 micron. If I am not mistaken I believe it is 98% at 2 micron.
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Highland Ridge Silverstar 378RBS