I dealt with this mystery for at least a year or so guys before my MAP sensor finally gave out altogether and threw my truck in reduced power mode one night. I then limped the truck to AutoZone, got a new MAP sensor thrown in there and it was like a brand new truck again! Haven't had a P0300 code since!
Definitely check your MAP sensor guys,(and the MAF for that matter too!) they can and will go bad on you with little to no warning, also check your battery if it's at least 3 years old or older. These trucks go nuts when the battery starts going south and P0300 error codes are common when that happens.(amongst other error codes, hah!) Another thing to look for I've found with the wiring harness/plug for my MAP is that the plug may have a short or loose/frayed wiring. A way to check this is to wiggle on the plug to the sensor while the truck is running. If the engine stumbles(and even throws an pending error code) you may want to replace the plug for the sensor as well.
Anyway, hope this helps, the sensors and electrical system of this truck are very touchy it seems. I'd start there when it comes to the P0300 code, at least you're not getting P030x codes right? (where it's a known cylinder misfiring)
2006 Chevrolet Colorado Regular Cab
Black w/sports pkg., 2WD, 2.8 I-4 w/ Manual Trans.
Last edited by Colly_shifter; 06-06-2012 at 10:09 AM.