If you have over 25K on your plugs they could be the problem. Yes a pound & a half can be enough to cause a misfire if your car was already near the edge.
I run a custom map 6 & ramped up 1/2 pound at a time with Terry reviewing the logs. Got to bad logs then backed down 1/2 pound.
2014 435M-Sport - 2013 135is Cab JB4/ISO 6MT - 2009 V-Star - 2009 Ford Expedition EL 4X4 - 2003 Xterra 4X4 - 1998 Ranger 4X4 - FFR Cobra MK-IV work in progress