I have a 99 f150 XL reg cab stepside bed 4.6 auto 4X4

I have this problem when i step on the gas to go, the first couple of second while starting to move i get this wiggle and if I look at the 4 wheel drive lever is shacks back and forth then stops as i am now moving from the innersa of being stopped. The more weight I have in the truck the more pronounced it is. I have 94K on the truck and i do pull a 6 1/2 x 12" landscape trailler alot for moving lawn tractors around. I thought the it might be axle rap but i am thinking that that is not it. Then there is full load of weight in the truck, the leaf springs are loaded and therefore how could they move? I have had this truck loaded many times and sometime i had stone in the back and it was very heavy, just about to the bump stops and it did it then too. But with weight in it, i would not think the axle rap would be as bad as empty. when it is empty it is not as noticable but if you take off fast you can feel this bump, and the shift lever for the 4 wheel drive shacks a couple times after taking off. It is really buzar... I have lookat the drive leaf springs, they look ok, no breaks, no bending anware, the motor mount are ok. I checked the trans mount and it looked ok. I am not shore!!! Mayby the drive shaft? I did notice on the drive shaft this funky universal joint that looks like a double nuckle going into the trans, could that be bad? Any info woul dbe great. I ahve takin it to a dealer and they said they could not dupicate it? I dont know!!! thanks for reading this and thanks again for your replies.

 

Sounds like a brocken transmission mount to me. I have never heard of axle wrap making your whole drivetrain move. BTW, axle wrap just doesnt appear, it usualy comes after adding a rear lift block.

 

eveything is stock on this truck except the exhaust and KnN air filter. Thanks i know it is buzzar..........