Transmission jerk.

I have a 2006 GMC 2500 crew cab with a duramax diesel, I pull a 10,000 pound 5th wheel. My problem is transmission jerk while towing. Whenever I let off on the gas it feels like the tranny skips, I'll be traveling along and it randomly jerks feeling like I ran over a bump or something. I don't know what this is and it bothers me. I had a 2001 Chevy with a duramax and that truck did the same thing. A fellow camper told me to try towing without using the "tow mode". Does any of you have any thoughts? This just doesn't seem like it should be normal to me.