First post, but have been getting great info on here for some time. I recently bought a 2004 Silverado 2500 4X4 with the 6.0 liter, 102,000 miles. Bought it at a dealer and didn't have it home for a full day before the check engine light came on. (bought as-is, did not add extended service plan) P0300, random multiple misfire. Funny thing was there was no noticeable misfire or miss. Ran great, plenty of power. It would only trip a code after about 10-15 minutes of highway driving (71 mph/ 2300-ish rpm). Driving for hours in town, accelerating/decelerating, test driving at dealer , would not trip it. Noticed the freeze frame data was all over the place, with large negative fuel trims, then large positive, etc. After reading many posts on here, I ran across a post with an issue similar to mine. I replaced the crankshaft position sensor, then took it to a dealer, who charged 59.99 to do the relearn procedure. And BOOM, no more misfire. Just wanted to share that info, hopefully it helps someone.

 

I have a similar issue with my 2005 k2500 6.0 gas ,, it seams like there is a clock attached to mine, every 2 weeks I get the p0300 code , I have misfire history on 1,5,6,8 swapped plugs ,wires, coils to see if cylinders change ,, same deal, did you have to do the relearn when you did the crank sensor ?

 

sorry so late....haven't been back on for a while. Yes, you have to have the relearn procedure done if crank position sensor is replaced. I don't know what exactly fixed my problem, either the replacement of the sensor or the relearn, but I have had no issues since.