Legit question. I have a 2004 F-150 that has been a great run around town light duty hauling truck, very dependable. Im now looking to up grade the engine with bolt on parts to increase power, nothing killer. The plan is to pull a 4000lbs trailer with this rig, well within factory specs. Suggestions/recommendations.

Sell it and buy a silverado with a 6.0 liter

supercharger

That 4r70 transmission will be the weak link. The engine should have enough power to get the job done, but it will be hard on everything.

The absolute best thing you can do is final drive gearing. That helps the transmission live, and makes the tow a LOT easier. BUT...you may have to use a tuner to adjust the transmission shift points among other things.

majority of aftermarket goodies improve power above peak torque and not below. The exceptions to that would be forced induction. You "could" use a set of 32v heads (make sure to get the right ones as there are at least 3 different designs) and front cover, then the blower/intake from a Cobra. That would wake it up, but it will also get a little more "peaky". But honestly, gearing will help tremendously, and if 4x2, inexpensively.