this sound like Standpipes and Dummy plugs?
had a very bad vibration at freeway speeds with Motorcraft 15w40, switched to T6 with archoil and its still there but not nearly as noticeable. It has new ficm, and starts fine when cold. hot starts always take more crank time, but was usually 1-1.5 sec or less. once in a while, hot starts take 5-7 sec, and yesterday had about a 12 sec crank to get it to start hot. (long cranks are maybe 1-2 times a week)
the dealer did the contribution thing and 1, 2, and 3 injectors were a little bit weaker than the rest of them but still normal. (all at front)
im thinking that the dummy plugs are drainging my HPO before it can fire the front injectors properly.
anyone have an opinion on this? also would STC fitting have this kind of symptoms by chance, or would it be an absolute no start?