2002 Dodge Ram Diminishing Performance

I recently learned this truck has no "in-line" fuel filter. I bought the truck new and have experienced no problem until now. The truck has been showing signs of increasing sluggishness in starting, in performance traveling down the road and a significant decrease in fuel mileage. I recently had it tuned up at the dealer. It has a new air filter, oil has been changed faithfully at 3000 mile intervals. At times while accelerating it feels like it might be laboring to increase speed, and upon an initial "cold" start it idles rough and is taking a longer cranking duration to fire-up. Any thoughts? Thank you.