1997 GMC Suburban 5.7L P0300 Misfire Diagnosis and Solutions

Hi everyone, I recently installed a new 5.7L engine in my 1997 GMC Suburban (2,000 miles after installation) and completed several maintenance tasks myself — including replacing the A/C hoses, servicing the brakes (front and rear), and performing all work to cut costs and ensure quality. I purchased this Suburban from a neighbor with 130,000 miles; the body and interior are in excellent condition. However, just two months later, I've started receiving a P030-0 misfire code. I’ve already replaced the fuel filter (which was clogged), but that didn’t resolve the issue. The vehicle currently sputters and stumbles at idle, runs smoothly after a few seconds, yet lacks power. I’ve checked spark plugs, distributor cap, rotor, and wires — all appear fine. I’m now considering replacing the fuel injectors, but I’d like to avoid spending that much money if possible. Can anyone help me pinpoint the root cause more accurately? The P0300 code indicates a random misfire across cylinders, which could stem from issues with ignition components, fuel delivery, or engine timing — especially in older 5.7L engines. Any insights into common causes or diagnostic steps for this specific model would be greatly appreciated. Thanks so much! Glenn