What would cause an 2003 Ford Expeditions engine to violently shake?

Changed the spark plugs, the oil filter, air filter, catalytic converter on both sides and ac vent accuator. For a while now the car would shake and sometimes cut off while idle. Then upon changing everything it was fine. Within the last 2 weeks when I turn the ac on it would shake like it wanted to cut off again. Today it started shaking so bad like I was being bumped at warp speed on all sides. The car wouldnt go over 20MPG. I barely made it home. The check engine light was blinking but wouldnt stay on. I have no clue what this could be. I changed everything I could find relating to the problem but now it seems it is worst then before. What is going on with it? Its a 4.7 engine with 198,000 miles. Is my engine garbage or can I fix it? I do not have thousands to spend for a mechanic to search for gold under my hood, But I need my car.

A blinking check engine light means shut the car off immediately. You have an excess fuel problem that melted your converters. Replacing them remedied your exhaust blockage but failing to fix the original problem has probably ruined your new converters.
Converters are there to burn off any unburned fuel. Normally there's very little of this so they stay within normal temps. A fuel issue can put a lot of unburned fuel into the exhaust causing the converters to really heat up and melt the ceramic matrix.
A misfiring cylinder can cause this very condition. This actually happened to me last week from a bad plug wire. Reading the engine codes should have been first priority to find root cause.

Probably only half the engine is running. OBD2 will tell you more than we ever can.

An OBD2 code check should tell you what went wrong. It is not motor mounts. They hold the engine in place but have nothing to do with how it runs or doesn't run.