Hard Transmission Down Shift

[remark2013]

I have a 2001 Ford F-350 CC Dually with ~190,000 miles on her. She has a John Wood TowMaster with about 50,000 miles on it. I have a Wicked Wheel II and a Riff Raff open Air Cleaner, man can she sing! I have downloaded multiple towing tunes, both with modified valve body and without a modified valve body.
My problem is when the truck downshift while pulling a load, a 24' enclosed car hauler with 2 Can-Am Spyders each approx. 1000 lbs. so guessing 5000 lbs., it slams the transmission hard enough to shake the truck going down the road. I have selected both the non modified as well as the modified valve body tunes and both have the same results. In Stock setting transmission downshift just fine, nice and smooth. Can anyone give me an idea of what tune to try next time I tow other than Stock?
Thank you in advance, Remark2013!