Two things to try are switching the number 6 injector with one from a different cylinder to see if the misfire moves to that other cylinder, and check the routing of the plug wires. If any are too close together, the current through one can induce a voltage spike into another one causing that plug to fire at the wrong time.
Misfires are detected by the rotational speed of the crankshaft slowing down momentarily. That is what allows us to feel it. At highway speeds that may not last long enough to be detected, but the misfire event will last longer at slower speeds and that may be the only time it is detected.
Friday, October 26th, 2012 AT 9:15 PM