p0300 random missfire puzzle

[HalfTon]

Well I bought what seemed to be one of my dream trucks. 1999 chevy reg cab short bed, 4x4, 5 speed, and with a 4.8. I knew the truck had some issues but nothing serious. 300 miles after buying it the SES came one with p0300. eventually the light began to flash but I never noticed a lack in power. My scanner is just a basic one so it will only give me freeze frame data, so i cannot determine which cylinders are supposedly missfiring. I started with the basics and replaced:
plugs and wires
checked fuel pressure regulator
changed fuel filter
fuel presssure is in spec
no vacum leaks found
cleaned maf, throttle body, and k&n air filter
all coil packs are producing spark
Where should I go from here?? the truck idles and starts fantastic and I have never actually felt the engine missfire. If I clear the code, sometimes it will stay of for 50-60 miles and other times it will come back within 7mi.
What do you guys think I should try next?