Markwl

I have an '02 Supercrew, V8, with 188,000 miles on it. It's been running great and is driving smooth but have noticed a drop off in fuel economy recently. Used to get 385-400 miles per tank now seeing 330-340 per tank. New tires, new tranny 50,000 miles ago . . . last oil change saw dirty fuel filter. Replaced filter and have used some gas treatments at fill up with no increase in fuel efficiency. Is a bigger problem looming (fuel pump, fuel line issues, injectors, sensors, etc??) Any help would be appreciated. I'm not very knowledgeable on cars/trucks and am looking for some direction before I take it in to mechanic. Thanks.

AFSOCSGT

Gas treatments can foul spark plugs, may need to change them. Mine did the same thing due to treatments.