yea i thought the same thing about it doing it only in that gear. im no professional with a auto but it may be your tc. im to the point now where i will try anything bc its really annoying mine only does it when my trailer is loaded and i tow almost everyday.

 

could u get a vid of it? maybe if i could see it and hear it i could help but to me sounds like its urtruck not liking the weight of the trailers or maybe just maybe check ur studs on ur tires... i had a 01 with 6 of 8 broken off and it would do that.... just a idea

 

I get the same thing hauling ONLY the 30' gooseneck, for me it's axle wrap. If I let off I can feel the truck settle and stop jerking, and if I hammer down I can feel the springs preload even more.