i have an f250 with a 150 frame. auto trans, 5.4 engine. 136K miles. it surges between 40 and 45 in a way that makes the steering wheel bounce back and forth. it does it accelerating and decelerating. it even does it when coasting in neutral. when i accelerate with "vigor" it hardly vibrates at all. i jacked up the front end to see if the new tires are out of round. did the same to the rear end; with one tire still on the ground wheels chocked. it roared loudly through the axle. did the other side...roared the same way. with both wheels off the ground it was quiet. the rear was engine idle in drive, no park brake. the front pinion shaft is tight, no wobble at all. a few days ago i put 6 75lb bales of hay in the bed and it drove without any vibration all the way to the barn... off loaded the hay and it begins again. i even had my torque converter checked at a tranny shop... it's ok. any one have a like experience or know what my problem is??