clunking from t-case?

very low speeds there is nothing. but getting up to about 15-20 and soon as i let off the gas i am getting a clunk from underneath. Hitting the brakes it gets 10x worse. pulled both driveshafts and it only does it when rear is in. u-joints seem ok, no slop. transfer case problem?

Transmission mount?

Are the u-bolts on the rear axle tight?

Bad U Joint?

u-joint was my first guess. but there is no play at all in it. all mounts seem to be good. havent looked at u-bolts. after driving more it really feels like its coming from right under me.

Transmission mounts can fool you, they look good but "collapse". When under torque the rear of the transmission can move quite a bit. Get a floor jack, place a piece of wood on the saddle--to protect the case--and jack up the rear of the transmission right in front of the crossmember. There really shouldn't be any movement when jacking it up--it isn't designed to "flex" or "stretch".