This only occurs when I pull anything. There is a shudder, like a heavy vibration - can't tell if it's from the front or rear - starting at about 35 mph and most prominent at 55 mph. It comes and goes - that is, one day it wont do it and the next day it starts again. Putting it in nuetral does not make a difference...different tires did not help either. Maybe the rear end???? If I can't solve this problem, I am going to sell this thing! I have 140,000 trouble-free miles on it...I only tow a trailer occasionally, but when I need it, I need it to work well. Any suggestions??