95 dodge 2500 that the front end starts to junp violently at 40 mph.

You might need a tire balanced or a have a bad cord in a tire.

There are a number of places to look for the answer. Check your motor mounts to see if they are broken. When you hit a certain speed the torque of the engine can lift the motor mount apart. Also check the transmission cross member for a loose connection to frame. Chek the tail shaft of the transmission to see if the bolts have fallen out.

This is a symptom of a badly worn track bar.