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?

[grumpyolddog]

My 2002 gmc 4.8, two wheel drive 5 speed pops this code if I gear down to slow the truck down in second gear. I know it does it but it sounds so good, flowmaster 40. Just clear the code maybe every six weeks lol

[HalfTon]

Mine doesnt really have any specific time for it to come on. I clear the code and it will come back within 30mi yet I I never feel any cylinders actually missing. Unfortunately I have to get emissions test to get it registered in my area so I'm trying to get this fixed asap

[LakeAnna]

My 2002 5.3 had that code and another I cannot recall after doing a Blackbear tune. I had to have a buddy hook up to it and do a Crank Relearn and it cleared it. Maybe the pcu in that one was switched at some point.... Just an idea.

[HalfTon]

forgot to update the thread. I did fix the code by having a crank relearn. has been off for about a week now.

[HemiChallenger71]

Bumping this, I too have fixed a po300 code with a crank re-learn on several LS powered vehicles.

[ChrisC10]

I recently bought a 2002 CCSB 2500HD, 6.0L. It had quite afew things wrong with it and I am stillfixing things. It needed a new rear knock sensor (which I changed both with some aftermarket ones and awiring harnes...mistake because then it said I needed both sensors replaced and had to take it all apart again)

It also has....still has the p0300 code. I have changed the plugs and wires which it really needed. I also changed the instake gasket when I did the knock sensors. I still need to fix the exhaust manifold bolts that are broke off. It has 3 on the passenger side and 2on the drivers side. It has a pretty nasty exhaust leak on the passenger side.

Blah blah blah....long story short.... do you guys think my issue might be a crank relearn? I get a flashing CEL only around 50-55mph and if I let off a bit and get the rpms back under 2000 it stops. It seems to only set it off under load. I can't really ever feel it missing. It is lifted with 35" tires that probably need balanced. It also needes tie rod and ball jointson the passenger side. It has 165000 miles too.

I guess I'm still rambling but just trying to give as much information as I can.

Thanks Chris (sorry tohi-jack this thread with my problem.)