not to insult in any way... but not knowing how you check your plugs, i would offer this.
i was always told this:
first, make sure your timing and valves are adjusted correctly.
Then take the car on a twenty mile run to make sure it is good and warmed up. the last ten miles don't let the car go under 2500 RPM's. if you have to slow down, shift down but keep the rpm's up. No idling. when you get to a place at the end of those ten miles you can pull off, shut off the engine and drift to a stop. lift the hood and check the plugs.
This gives your car time to clean up the plugs and a more accurate check of what the car is doing at speed. better for the car to run a little rich around town than to run lean at speed.
i have a place 10 miles from home i drive to and then turn around. on the way home i keep the RPM's over 2500. when i get back to my drive, i shut off the engine and drift to the shop. let the car cool a little and then pull the plugs. i know other guys who have taken their plug wrench with them because the have to stop going home.