Also check the obvious. Make sure the right plug wire goes to the right plug.
Several years ago, I was interested in buying an Olds Ciera that the owner proudly proclaimed had had a new engine (V6) installed two years and had only 26,000 miles on it. I ran it into my shop to check it out. I had a seat-of-the-pants feeling that something wasn't quite as smooth as it should have been. I traced out the plug wires and, you guessed it, two were reversed.
This guy had driven the car 26,000 miles with the plug wires scrambled! I passed on it.