i know the OP said he’d check a few others things but I’d circle back to what BadlandsA51 said here. I’m pretty sure 3” exceeds what fords tolerances are. I need to check but something under 1.5” comes to mindIf you did a 3" spacer and didn't do anything to lower the front differential there is a good chance the vibration is coming from the inner plunge joints on the half shafts. A 3" lift will increase the angle of the half shafts quite a bit and the inner joints aren't true CV joints so they will set up a vibration. The vibration should get a little worse under hard acceleration if the half shafts are the cause. That would be due to the front end lifting during acceleration causing the angle to increase.
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