1st switch to Synthetic oil... Shell Rotella TRIPLE protection is readily available and has 1200 ppm of Zinc/Phosphate ( you want this for flat tappet cams)
2nd swap to a colder t-stat... 180° for California emisions or colder 160° for eastern emissions.
Next I would take the muffler off the truck and just run from the cats... I saw more gain running a full exhaust with NO muffler and an empty rear cat... although in Emissions checking states you may not be able to do this...
Next do the timing bump with a Brass cap and rotor.... good wires like the MSD streetfire or the Taylor Spiro-pro...
next rip off the clutch fan and convert to E-fan...
you'll free up a bit more than 40hp doing all those
Check with the guiys over at the Ford six performance site.
On mine I have the low resistance wires, timing bump to 12 deg, spark gap at .050, and keep the oil and filters clean.
The big restriction in this engine is the cylinder head and nothing that you can plug in or bolt on will help much until you clean it up.
Electric fans can help but make sure your alternator can handle the load.
BTW your engine already has a CAI, and the stock manifolds are pretty good. High flow cats and a straight pipe out the side would probably help. Beware that some performance mufflers can make the 300 sound pretty strange.