What causes an engine to shake after changing the spark plugs?

Sounds like plug wires were swapped plug to plug or a wire got damaged pulling it off. I have swapped plug wires before on accident and now do them one at a time. That is pulling only one wire and replacing one plug at a time before going to the next one. You might trying looking under the hood in total darkness at night or whatever and see if you see and wires arcing to a ground anywhere from the dist/coil/plugs. Go to the part store and get the firing order for the motor if you suspect you may have swapped a couple of wires. I just saw it was an Expedition as well it may have no wires and be coil on plug on every cylinder. Coil boots are replaced every tune up on some as well. You may have left a vacuum line off somewhere or bumped one as well. Listen for suction or hissing type noise.