So yours only does it on deceleration? Mine always does it accelerating through that range but on decelerating it is different. If I decelerate slowly like by lifting a wee bit on the throttle it will get through that range with no issue but if I lift completely off the throttle it vibrates just as much as if I were accelerating. I figure it has to be driveline related somewhere but I don't know what else to check.

The larger tires are on my agenda. Current is 245/75 and I plan to go to at least 265/75 which if nothing else will raise the actual speed at which it happens.

It's a funny deal. My 1996 5 speed Troop doesnt do it and the tires on that truck are puny little original size ones.