P0300 Random/Multiple Cylinder Misfire Detected

[Hammer]

I´m on a long road trip far away from home (2000miles away) and hummer failed me today gave the p0300 code and started running reallly rough just all of a sudden when driving aroung 40mph. Any ideas. :(
Truck have 55000 miles...

[Biskxp]

had that issue when one of my cats was failing.

[Hummeron37s]

same here had the code when my cat converter failed

[HumminNBoatin']

When my cats went I did not get that code. But mine did go out at almost the same mileage you have now. Typically when cats are going out you get O2 sensor codes. However if those guys had that code when cats went I would check there first. Then go pulling spark plugs and check if your cats are clear. If it is truly ignition i would replace plugs and cam/crank sensor.

[Hammer]

This happened after I had some deep snow fun moment earlier.
Goin to do just regular maintenance first hope it helps. Plug wires, Fuel filter, maybe plugs if thy look bad.

[Xotik H3]

The problem will be common to all cylinders - cat, fuel filter, timing crank sensor... forget the plugs and wires.