What happens during braking? Does it make any sounds when you let off the gas? I really don't think the little fan has enough inertia to move the front of the vehicle. If that was the problem, all Bronc's with engine driven fans would experience this. This was pretty common during WWI with the old bi-planes that had radial engines and 8' props, though. Never heard of it in a car.
It sounds like something is happening when weight is transferred to the front when decelerating. This could be a worn or missing track bar bushing, or mayne a "C" bushing or radius arm bushing. I would start with those, and then move to the kingpin or ball joints, whichever you have. Do you have a lift? Then check the angle of the drag link and track bar. They should be paralell. Also make sure your tires are properly inflated and are the same type and with equal wear. If all else fails, replace the 2-speed muffler bearing and take for a test drive.