what is the main problem with the ford excursion to cause a vibration in the drive line?

What is your question?

excursion has a heavy vibration thru out the vechicle when ever you go into an idle at 35 mph and at idle at 55 to 70 mph. Had pinion bearing in rear end checked, now checking torque converter. What is your opinion on this problem?

What makes this problem better or worse?

nothing is there at all times when driving or towing.

How long has your 2001 Ford Excursion had this problem?

just bought it so about 3 months