Trouble code P0300

Hi, I just had the unit scanned and it came back with P0300 - Cylinder misfire(random)
The plugs have not been changed in 2 years so is that a good starting point? The vehicle has only 100,000 miles and is a 2000 Jimmy Diamond Edition 4.3 L
The trouble light usually resets after a week or so but comes back on when highway driving up long hills.
Any pointers greatly appreciated.
Thanks, Rick

Random misfires -
Do a little routine maintenance.
New fuel filter, Air filter, and clean throttle body.

P0300 series DTC's are almost always caused by secondary ignition faults: distributor cap, distributor rotor, spark plug wires, spark plugs, and ignition coil. The 4.3 is quite fussy when it comes to these parts. Stay away from aftermarket stuff and use AC Delco, especially the plugs, cap and rotor. At 100,000 miles all of these items should be replaced, along with the oxygen sensors, air and fuel filters. It's a good idea to check fuel pressure and leakdown also... anything over 100,000 miles on the fuel pump is a bonus. Again, AC Delco, don't waste your time or money on anything else.

Thanks, I'll start with plugs, cap and rotor.