P0300 Misfire in 1996 S10 4.3L: Surging at Cruising Speed - EGR Valve Diagnosis?

I recently purchased a 1996 Chevrolet S10 with a 4.3L V6 engine and 162,000 miles. The truck was not running initially, and I discovered a shorted coil wire. I replaced the rotor, spark plugs, ignition wires, and also fixed a stuck-open thermostat. After these repairs, it ran smoothly for approximately 3,000 miles. However, recently I've started experiencing surging when the gas pedal is gently pressed to maintain cruising speed. I initially ignored this issue and have been using more throttle or avoiding light acceleration to prevent the surge. Today, during a vehicle inspection, the truck triggered a P0300 misfire code before I even got there! This happens regardless of temperature—both hot and cold—and occurs consistently while cruising. I plan to clear the code temporarily, but I'm concerned about what's actually causing this behavior. Should I investigate the EGR valve? The symptoms suggest a lean condition or fuel delivery issue during steady-state driving, which could be linked to an EGR leak. While I've replaced several components, the persistent P03-than-expected surging raises concerns about underlying engine performance issues.