if it started after you swapped the TFI module, go buy a new one. Since you can feel it as well as see it on the tach, it's not the tach. I doubt it's the coil, either. The tach registers competed ignition circuits, which is why you will see a dip in the needle if you have a fouled plug. Just because it's wired before the coil, doesn't mean everything after the coil is good.
Sounds like a TFI module to me.
Take care,
-Chris
------------------
Retired Moderator
MustangNet
My site:
Peckerwoods Pit Stop
My teams site:
Jim Porter Racing
RACECAR spelled backwards is RACECAR
HEY !!! Are you ASE Certified ??? If you are, ask me about iATN.