P0300 Code

I searched the forum for the following problem, but didn't find anything that quite matched it so here goes.

2000 5.3 w/ 97k miles - SES light comes on steadily (as in not flashing) when the truck is under a load (either bed is loaded or pulling a trailer) and will go out sometime after the truck has been running empty for a while. I checked the SES codes the last time this happened and the only code listed was P0300. I can not feel any mis-fire nor do I notice any loss in power or stumbling when or after the light comes on. I changed the plugs & wires at 94k miles and it's got a k&n filter and gibson exhaust. Any suggestions would be greatly appreciated.

Thanks in advance.

A P0300 can be caused by alot of different events. Sometimes not even related to an actuall misfire condition. I would hook up the mastertech scan tool. let the SES clear itself (or clear it with the scan tool). Then do a road test with scan tool monitoring the whole drive cycle. Hopefully the SES light will come on again during the drive cycle. Then you can look at the history record of tool to get an idea to narrow down cause. I hate the P0300-308 codes, some are so difficult to troubleshoot.