Okay, 2003 Mustang GT, 4.6L. Completly stock outside of transmission. Last week, threw codes for engine misfire, changed out ignition coils and spark plugs and issue seemed to go away at idle, however I didn't get a chance to drive it that day due to snow. Finally took it out today, seemed okay at first, but then seemed like it still had a little bit of a misfire (I will also mention that a few of the electrical connectors for the ignition coils did break when they were removed, but were still making good connection from what we could see, as I've seen this happen on many 4.6L's that run fine)but anyway, the misfire seemed very minor at first. Eventually I shifted into 5th at around 45-50 MPH, which dropped the RPM's to around 1000-1150 or so. At this point, the shifter itself started shaking violently, along with the engine, tranny (from what I could feel) and pretty much the whole car in general. As soon as I put the clutch in, it stopped, and I didn't notice it in any other gear unless I shift early and the RPM's drop. Never felt a misfire this severe before, and its not throwing any engine lights or anything like that. Any idea's? Thanks!