[Country Suburban 4x4]

How many miles are on your truck? And does the engine actually feel like it is misfiring? Or does it still run smooth? The 99-06 trucks have been known to throw the po300 after 120,000+ miles because the timing components wear, but the crankshaft position sensor still reads to the factory specs. This causes it to think there is a misfire under long driving times, or under heavy load. I went through this with my Silverado. The engine runs amazing at 170k miles with no sign of misfire. I'm not saying that this is definitely your issue, plugs and wires wouldn't hurt. But if it is the same issue, you'll have to go in with a scan tool and do a re-learn on your crankshaft position sensor. Hope this helps.