So you're saying that early coil failure feels like a vibration rather than a miss? Usually a guy can tell the difference between an engine misfire and driveline vibration.

 

Early failing coils are normally not felt at all. Of course they're wasting fuel, messing with trims and damaging cats.

 

Is it constant vibration once it starts or it cycles on and off?
If constant at said 45mph then I would side with ignition coil, but if it cycles, I would look into transmission fluid - it could be the transmission clutch chatter.
If it's chatter, this product is endorsed widely: LUBEGARD Automatic Transmission Fluid Protectant

 

Your asking questions that can't be answered because it all depends.

Go get the codes read so we have something concrete to look at. Your descriptions don't do any good!
.
.
.