[shorod]

Welcome to the forum!

If you have access to a professional-grade scan tool, get into the component parameters and monitor the misfire PIDs for each cylinder. Maybe you have a coil or two that is failing under load. Does the roughness only occur at idle, or when driving as well?

Also, have you ever cleaned the Mass Air Flow (MAF) sensor? Do you have any modifications to the engine of your Sport Trac (such as a K&N or similar air filter)? Do you regularly use fuel injector cleaner?

-Rod